/usr/share/doc/python-attr/html/api.html is in python-attr-doc 17.4.0-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>API Reference — attrs 17.4.0 documentation</title>
<link rel="stylesheet" href="_static/alabaster.css" type="text/css" />
<link rel="stylesheet" href="_static/pygments.css" type="text/css" />
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: './',
VERSION: '17.4.0',
COLLAPSE_INDEX: false,
FILE_SUFFIX: '.html',
HAS_SOURCE: true,
SOURCELINK_SUFFIX: '.txt'
};
</script>
<script type="text/javascript" src="_static/jquery.js"></script>
<script type="text/javascript" src="_static/underscore.js"></script>
<script type="text/javascript" src="_static/doctools.js"></script>
<link rel="index" title="Index" href="genindex.html" />
<link rel="search" title="Search" href="search.html" />
<link rel="next" title="Extending" href="extending.html" />
<link rel="prev" title="attrs by Example" href="examples.html" />
<link rel="stylesheet" href="_static/custom.css" type="text/css" />
<meta name="viewport" content="width=device-width, initial-scale=0.9, maximum-scale=0.9" />
</head>
<body>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<div class="section" id="api-reference">
<span id="api"></span><h1>API Reference<a class="headerlink" href="#api-reference" title="Permalink to this headline">¶</a></h1>
<p><code class="docutils literal"><span class="pre">attrs</span></code> works by decorating a class using <a class="reference internal" href="#attr.s" title="attr.s"><code class="xref py py-func docutils literal"><span class="pre">attr.s()</span></code></a> and then optionally defining attributes on the class using <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">When this documentation speaks about “<code class="docutils literal"><span class="pre">attrs</span></code> attributes” it means those attributes that are defined using <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a> in the class body.</p>
</div>
<p>What follows is the API explanation, if you’d like a more hands-on introduction, have a look at <a class="reference internal" href="examples.html"><span class="doc">attrs by Example</span></a>.</p>
<div class="section" id="core">
<h2>Core<a class="headerlink" href="#core" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="attr.s">
<code class="descclassname">attr.</code><code class="descname">s</code><span class="sig-paren">(</span><em>these=None</em>, <em>repr_ns=None</em>, <em>repr=True</em>, <em>cmp=True</em>, <em>hash=None</em>, <em>init=True</em>, <em>slots=False</em>, <em>frozen=False</em>, <em>str=False</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.s" title="Permalink to this definition">¶</a></dt>
<dd><p>A class decorator that adds <a class="reference external" href="https://wiki.python.org/moin/DunderAlias">dunder</a>-methods according to the
specified attributes using <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a> or the <em>these</em> argument.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple">
<li><strong>these</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#dict" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">dict</span></code></a> of <a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#str" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">str</span></code></a> to <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a>) – <p>A dictionary of name to <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a> mappings. This is
useful to avoid the definition of your attributes within the class body
because you can’t (e.g. if you want to add <code class="docutils literal"><span class="pre">__repr__</span></code> methods to
Django models) or don’t want to.</p>
<p>If <em>these</em> is not <code class="docutils literal"><span class="pre">None</span></code>, <code class="docutils literal"><span class="pre">attrs</span></code> will <em>not</em> search the class body
for attributes.</p>
</li>
<li><strong>repr_ns</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#str" title="(in Python v3.6)"><em>str</em></a>) – When using nested classes, there’s no way in Python 2
to automatically detect that. Therefore it’s possible to set the
namespace explicitly for a more meaningful <code class="docutils literal"><span class="pre">repr</span></code> output.</li>
<li><strong>repr</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Create a <code class="docutils literal"><span class="pre">__repr__</span></code> method with a human readable
representation of <code class="docutils literal"><span class="pre">attrs</span></code> attributes..</li>
<li><strong>str</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Create a <code class="docutils literal"><span class="pre">__str__</span></code> method that is identical to
<code class="docutils literal"><span class="pre">__repr__</span></code>. This is usually not necessary except for
<a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#Exception" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">Exception</span></code></a>s.</li>
<li><strong>cmp</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Create <code class="docutils literal"><span class="pre">__eq__</span></code>, <code class="docutils literal"><span class="pre">__ne__</span></code>, <code class="docutils literal"><span class="pre">__lt__</span></code>, <code class="docutils literal"><span class="pre">__le__</span></code>,
<code class="docutils literal"><span class="pre">__gt__</span></code>, and <code class="docutils literal"><span class="pre">__ge__</span></code> methods that compare the class as if it were
a tuple of its <code class="docutils literal"><span class="pre">attrs</span></code> attributes. But the attributes are <em>only</em>
compared, if the type of both classes is <em>identical</em>!</li>
<li><strong>hash</strong> (<code class="docutils literal"><span class="pre">bool</span></code> or <code class="docutils literal"><span class="pre">None</span></code>) – <p>If <code class="docutils literal"><span class="pre">None</span></code> (default), the <code class="docutils literal"><span class="pre">__hash__</span></code> method is generated
according how <em>cmp</em> and <em>frozen</em> are set.</p>
<ol class="arabic">
<li>If <em>both</em> are True, <code class="docutils literal"><span class="pre">attrs</span></code> will generate a <code class="docutils literal"><span class="pre">__hash__</span></code> for you.</li>
<li>If <em>cmp</em> is True and <em>frozen</em> is False, <code class="docutils literal"><span class="pre">__hash__</span></code> will be set to
None, marking it unhashable (which it is).</li>
<li>If <em>cmp</em> is False, <code class="docutils literal"><span class="pre">__hash__</span></code> will be left untouched meaning the
<code class="docutils literal"><span class="pre">__hash__</span></code> method of the superclass will be used (if superclass is
<code class="docutils literal"><span class="pre">object</span></code>, this means it will fall back to id-based hashing.).</li>
</ol>
<p>Although not recommended, you can decide for yourself and force
<code class="docutils literal"><span class="pre">attrs</span></code> to create one (e.g. if the class is immutable even though you
didn’t freeze it programmatically) by passing <code class="docutils literal"><span class="pre">True</span></code> or not. Both of
these cases are rather special and should be used carefully.</p>
<p>See the <a class="reference external" href="https://docs.python.org/3/reference/datamodel.html#object.__hash__">Python documentation </a>
and the <a class="reference external" href="https://github.com/python-attrs/attrs/issues/136">GitHub issue that led to the default behavior </a> for more details.</p>
</li>
<li><strong>init</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Create a <code class="docutils literal"><span class="pre">__init__</span></code> method that initializes the
<code class="docutils literal"><span class="pre">attrs</span></code> attributes. Leading underscores are stripped for the
argument name. If a <code class="docutils literal"><span class="pre">__attrs_post_init__</span></code> method exists on the
class, it will be called after the class is fully initialized.</li>
<li><strong>slots</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Create a <a class="reference external" href="https://docs.python.org/3/reference/datamodel.html#slots">slots</a>-style class that’s more
memory-efficient. See <a class="reference internal" href="examples.html#slots"><span class="std std-ref">Slots</span></a> for further ramifications.</li>
<li><strong>frozen</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – <p>Make instances immutable after initialization. If
someone attempts to modify a frozen instance,
<a class="reference internal" href="#attr.exceptions.FrozenInstanceError" title="attr.exceptions.FrozenInstanceError"><code class="xref py py-exc docutils literal"><span class="pre">attr.exceptions.FrozenInstanceError</span></code></a> is raised.</p>
<p>Please note:</p>
<blockquote>
<div><ol class="arabic">
<li>This is achieved by installing a custom <code class="docutils literal"><span class="pre">__setattr__</span></code> method
on your class so you can’t implement an own one.</li>
<li>True immutability is impossible in Python.</li>
<li>This <em>does</em> have a minor a runtime performance <a class="reference internal" href="how-does-it-work.html#how-frozen"><span class="std std-ref">impact</span></a> when initializing new instances. In other words:
<code class="docutils literal"><span class="pre">__init__</span></code> is slightly slower with <code class="docutils literal"><span class="pre">frozen=True</span></code>.</li>
<li>If a class is frozen, you cannot modify <code class="docutils literal"><span class="pre">self</span></code> in
<code class="docutils literal"><span class="pre">__attrs_post_init__</span></code> or a self-written <code class="docutils literal"><span class="pre">__init__</span></code>. You can
circumvent that limitation by using
<code class="docutils literal"><span class="pre">object.__setattr__(self,</span> <span class="pre">"attribute_name",</span> <span class="pre">value)</span></code>.</li>
</ol>
</div></blockquote>
</li>
<li><strong>auto_attribs</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – <p>If True, collect <a class="reference external" href="https://www.python.org/dev/peps/pep-0526/">PEP 526</a>-annotated attributes
(Python 3.6 and later only) from the class body.</p>
<p>In this case, you <strong>must</strong> annotate every field. If <code class="docutils literal"><span class="pre">attrs</span></code>
encounters a field that is set to an <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a> but lacks a type
annotation, an <a class="reference internal" href="#attr.exceptions.UnannotatedAttributeError" title="attr.exceptions.UnannotatedAttributeError"><code class="xref py py-exc docutils literal"><span class="pre">attr.exceptions.UnannotatedAttributeError</span></code></a> is
raised. Use <code class="docutils literal"><span class="pre">field_name:</span> <span class="pre">typing.Any</span> <span class="pre">=</span> <span class="pre">attr.ib(...)</span></code> if you don’t
want to set a type.</p>
<p>If you assign a value to those attributes (e.g. <code class="docutils literal"><span class="pre">x:</span> <span class="pre">int</span> <span class="pre">=</span> <span class="pre">42</span></code>), that
value becomes the default value like if it were passed using
<code class="docutils literal"><span class="pre">attr.ib(default=42)</span></code>. Passing an instance of <a class="reference internal" href="#attr.Factory" title="attr.Factory"><code class="xref py py-class docutils literal"><span class="pre">Factory</span></code></a> also
works as expected.</p>
<p>Attributes annotated as <a class="reference external" href="/usr/share/doc/python3-doc/html/library/typing.html#typing.ClassVar" title="(in Python v3.6)"><code class="xref py py-data docutils literal"><span class="pre">typing.ClassVar</span></code></a> are <strong>ignored</strong>.</p>
</li>
</ul>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.0.0: </span><em>slots</em></p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.1.0: </span><em>frozen</em></p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.3.0: </span><em>str</em>, and support for <code class="docutils literal"><span class="pre">__attrs_post_init__</span></code>.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 17.1.0: </span><em>hash</em> supports <code class="docutils literal"><span class="pre">None</span></code> as value which is also the default
now.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.3.0: </span><em>auto_attribs</em></p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last"><code class="docutils literal"><span class="pre">attrs</span></code> also comes with a serious business alias <code class="docutils literal"><span class="pre">attr.attrs</span></code>.</p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">attr</span>
<span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">_private</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="n">private</span><span class="o">=</span><span class="mi">42</span><span class="p">)</span>
<span class="go">C(_private=42)</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">D</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">x</span> <span class="o">=</span> <span class="n">x</span>
<span class="gp">>>> </span><span class="n">D</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go"><D object at ...></span>
<span class="gp">>>> </span><span class="n">D</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">s</span><span class="p">(</span><span class="n">these</span><span class="o">=</span><span class="p">{</span><span class="s2">"x"</span><span class="p">:</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()},</span> <span class="n">init</span><span class="o">=</span><span class="kc">False</span><span class="p">)(</span><span class="n">D</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">D</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">D(x=1)</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.ib">
<code class="descclassname">attr.</code><code class="descname">ib</code><span class="sig-paren">(</span><em>default=NOTHING</em>, <em>validator=None</em>, <em>repr=True</em>, <em>cmp=True</em>, <em>hash=None</em>, <em>init=True</em>, <em>convert=None</em>, <em>metadata=None</em>, <em>type=None</em>, <em>converter=None</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.ib" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a new attribute on a class.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">Does <em>not</em> do anything unless the class is also decorated with
<a class="reference internal" href="#attr.s" title="attr.s"><code class="xref py py-func docutils literal"><span class="pre">attr.s()</span></code></a>!</p>
</div>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple">
<li><strong>default</strong> (<em>Any value.</em>) – <p>A value that is used if an <code class="docutils literal"><span class="pre">attrs</span></code>-generated <code class="docutils literal"><span class="pre">__init__</span></code>
is used and no value is passed while instantiating or the attribute is
excluded using <code class="docutils literal"><span class="pre">init=False</span></code>.</p>
<p>If the value is an instance of <a class="reference internal" href="#attr.Factory" title="attr.Factory"><code class="xref py py-class docutils literal"><span class="pre">Factory</span></code></a>, its callable will be
used to construct a new value (useful for mutable data types like lists
or dicts).</p>
<p>If a default is not set (or set manually to <code class="docutils literal"><span class="pre">attr.NOTHING</span></code>), a value
<em>must</em> be supplied when instantiating; otherwise a <a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a>
will be raised.</p>
<p>The default can also be set using decorator notation as shown below.</p>
</li>
<li><strong>validator</strong> (<code class="docutils literal"><span class="pre">callable</span></code> or a <code class="docutils literal"><span class="pre">list</span></code> of <code class="docutils literal"><span class="pre">callable</span></code>s.) – <p><a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><code class="xref py py-func docutils literal"><span class="pre">callable()</span></code></a> that is called by <code class="docutils literal"><span class="pre">attrs</span></code>-generated
<code class="docutils literal"><span class="pre">__init__</span></code> methods after the instance has been initialized. They
receive the initialized instance, the <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">Attribute</span></code></a>, and the
passed value.</p>
<p>The return value is <em>not</em> inspected so the validator has to throw an
exception itself.</p>
<p>If a <code class="docutils literal"><span class="pre">list</span></code> is passed, its items are treated as validators and must
all pass.</p>
<p>Validators can be globally disabled and re-enabled using
<a class="reference internal" href="#attr.get_run_validators" title="attr.get_run_validators"><code class="xref py py-func docutils literal"><span class="pre">get_run_validators()</span></code></a>.</p>
<p>The validator can also be set using decorator notation as shown below.</p>
</li>
<li><strong>repr</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Include this attribute in the generated <code class="docutils literal"><span class="pre">__repr__</span></code>
method.</li>
<li><strong>cmp</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Include this attribute in the generated comparison methods
(<code class="docutils literal"><span class="pre">__eq__</span></code> et al).</li>
<li><strong>hash</strong> (<code class="docutils literal"><span class="pre">bool</span></code> or <code class="docutils literal"><span class="pre">None</span></code>) – Include this attribute in the generated <code class="docutils literal"><span class="pre">__hash__</span></code>
method. If <code class="docutils literal"><span class="pre">None</span></code> (default), mirror <em>cmp</em>’s value. This is the
correct behavior according the Python spec. Setting this value to
anything else than <code class="docutils literal"><span class="pre">None</span></code> is <em>discouraged</em>.</li>
<li><strong>init</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Include this attribute in the generated <code class="docutils literal"><span class="pre">__init__</span></code>
method. It is possible to set this to <code class="docutils literal"><span class="pre">False</span></code> and set a default
value. In that case this attributed is unconditionally initialized
with the specified default value or factory.</li>
<li><strong>converter</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – <a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><code class="xref py py-func docutils literal"><span class="pre">callable()</span></code></a> that is called by
<code class="docutils literal"><span class="pre">attrs</span></code>-generated <code class="docutils literal"><span class="pre">__init__</span></code> methods to converter attribute’s value
to the desired format. It is given the passed-in value, and the
returned value will be used as the new value of the attribute. The
value is converted before being passed to the validator, if any.</li>
<li><strong>metadata</strong> – An arbitrary mapping, to be used by third-party
components. See <a class="reference internal" href="extending.html#extending-metadata"><span class="std std-ref">Metadata</span></a>.</li>
<li><strong>type</strong> – <p>The type of the attribute. In Python 3.6 or greater, the
preferred method to specify the type is using a variable annotation
(see <a class="reference external" href="https://www.python.org/dev/peps/pep-0526/">PEP 526</a>).
This argument is provided for backward compatibility.
Regardless of the approach used, the type will be stored on
<code class="docutils literal"><span class="pre">Attribute.type</span></code>.</p>
</li>
</ul>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 15.2.0: </span><em>convert</em></p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.3.0: </span><em>metadata</em></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 17.1.0: </span><em>validator</em> can be a <code class="docutils literal"><span class="pre">list</span></code> now.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 17.1.0: </span><em>hash</em> is <code class="docutils literal"><span class="pre">None</span></code> and therefore mirrors <em>cmp</em> by default.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.3.0: </span><em>type</em></p>
</div>
<div class="deprecated">
<p><span class="versionmodified">Deprecated since version 17.4.0: </span><em>convert</em></p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.4.0: </span><em>converter</em> as a replacement for the deprecated
<em>convert</em> to achieve consistency with other noun-based arguments.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last"><code class="docutils literal"><span class="pre">attrs</span></code> also comes with a serious business alias <code class="docutils literal"><span class="pre">attr.attrib</span></code>.</p>
</div>
<p>The object returned by <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a> also allows for setting the default and the validator using decorators:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="nd">@x</span><span class="o">.</span><span class="n">validator</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">name_can_be_anything</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">attribute</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">value</span> <span class="o"><</span> <span class="mi">0</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s2">"x must be positive"</span><span class="p">)</span>
<span class="gp">... </span> <span class="nd">@y</span><span class="o">.</span><span class="n">default</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">name_does_not_matter</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">x</span> <span class="o">+</span> <span class="mi">1</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">C(x=1, y=2)</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="o">...</span>
<span class="gr">ValueError</span>: <span class="n">x must be positive</span>
</pre></div>
</div>
</dd></dl>
<dl class="class">
<dt id="attr.Attribute">
<em class="property">class </em><code class="descclassname">attr.</code><code class="descname">Attribute</code><span class="sig-paren">(</span><em>name</em>, <em>default</em>, <em>validator</em>, <em>repr</em>, <em>cmp</em>, <em>hash</em>, <em>init</em>, <em>convert=None</em>, <em>metadata=None</em>, <em>type=None</em>, <em>converter=None</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.Attribute" title="Permalink to this definition">¶</a></dt>
<dd><p><em>Read-only</em> representation of an attribute.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Attribute name:</th><td class="field-body">The name of the attribute.</td>
</tr>
</tbody>
</table>
<p>Plus <em>all</em> arguments of <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a>.</p>
<p>For the version history of the fields, see <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a>.</p>
<p>Instances of this class are frequently used for introspection purposes like:</p>
<ul class="simple">
<li><a class="reference internal" href="#attr.fields" title="attr.fields"><code class="xref py py-func docutils literal"><span class="pre">fields()</span></code></a> returns a tuple of them.</li>
<li>Validators get them passed as the first argument.</li>
</ul>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">You should never instantiate this class yourself!</p>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">attr</span>
<span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">C</span><span class="p">)</span><span class="o">.</span><span class="n">x</span>
<span class="go">Attribute(name='x', default=NOTHING, validator=None, repr=True, cmp=True, hash=None, init=True, metadata=mappingproxy({}), type=None, converter=None)</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.make_class">
<code class="descclassname">attr.</code><code class="descname">make_class</code><span class="sig-paren">(</span><em>name</em>, <em>attrs</em>, <em>bases=(<class 'object'></em>, <em>)</em>, <em>**attributes_arguments</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.make_class" title="Permalink to this definition">¶</a></dt>
<dd><p>A quick way to create a new class called <em>name</em> with <em>attrs</em>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>name</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#str" title="(in Python v3.6)"><em>str</em></a>) – The name for the new class.</li>
<li><strong>attrs</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#list" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">list</span></code></a> or <a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#dict" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">dict</span></code></a>) – A list of names or a dictionary of mappings of names to
attributes.</li>
<li><strong>bases</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#tuple" title="(in Python v3.6)"><em>tuple</em></a>) – Classes that the new class will subclass.</li>
<li><strong>attributes_arguments</strong> – Passed unmodified to <a class="reference internal" href="#attr.s" title="attr.s"><code class="xref py py-func docutils literal"><span class="pre">attr.s()</span></code></a>.</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A new class with <em>attrs</em>.</p>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last"><a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#type" title="(in Python v3.6)">type</a></p>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0: </span><em>bases</em></p>
</div>
<p>This is handy if you want to programmatically create classes.</p>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">C1</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">make_class</span><span class="p">(</span><span class="s2">"C1"</span><span class="p">,</span> <span class="p">[</span><span class="s2">"x"</span><span class="p">,</span> <span class="s2">"y"</span><span class="p">])</span>
<span class="gp">>>> </span><span class="n">C1</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="go">C1(x=1, y=2)</span>
<span class="gp">>>> </span><span class="n">C2</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">make_class</span><span class="p">(</span><span class="s2">"C2"</span><span class="p">,</span> <span class="p">{</span><span class="s2">"x"</span><span class="p">:</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">default</span><span class="o">=</span><span class="mi">42</span><span class="p">),</span>
<span class="gp">... </span> <span class="s2">"y"</span><span class="p">:</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">default</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">Factory</span><span class="p">(</span><span class="nb">list</span><span class="p">))})</span>
<span class="gp">>>> </span><span class="n">C2</span><span class="p">()</span>
<span class="go">C2(x=42, y=[])</span>
</pre></div>
</div>
</dd></dl>
<dl class="class">
<dt id="attr.Factory">
<em class="property">class </em><code class="descclassname">attr.</code><code class="descname">Factory</code><span class="sig-paren">(</span><em>factory</em>, <em>takes_self=False</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.Factory" title="Permalink to this definition">¶</a></dt>
<dd><p>Stores a factory callable.</p>
<p>If passed as the default value to <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a>, the factory is used to
generate a new value.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple">
<li><strong>factory</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – A callable that takes either none or exactly one
mandatory positional argument depending on <em>takes_self</em>.</li>
<li><strong>takes_self</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Pass the partially initialized instance that is
being initialized as a positional argument.</li>
</ul>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0: </span><em>takes_self</em></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">default</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">Factory</span><span class="p">(</span><span class="nb">list</span><span class="p">))</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">default</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">Factory</span><span class="p">(</span>
<span class="gp">... </span> <span class="k">lambda</span> <span class="bp">self</span><span class="p">:</span> <span class="nb">set</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">x</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">takes_self</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="gp">... </span> <span class="p">)</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">()</span>
<span class="go">C(x=[], y=set())</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">])</span>
<span class="go">C(x=[1, 2, 3], y={1, 2, 3})</span>
</pre></div>
</div>
</dd></dl>
<dl class="exception">
<dt id="attr.exceptions.FrozenInstanceError">
<em class="property">exception </em><code class="descclassname">attr.exceptions.</code><code class="descname">FrozenInstanceError</code><a class="headerlink" href="#attr.exceptions.FrozenInstanceError" title="Permalink to this definition">¶</a></dt>
<dd><p>A frozen/immutable instance has been attempted to be modified.</p>
<p>It mirrors the behavior of <code class="docutils literal"><span class="pre">namedtuples</span></code> by using the same error message
and subclassing <a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#AttributeError" title="(in Python v3.6)"><code class="xref py py-exc docutils literal"><span class="pre">AttributeError</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.1.0.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="attr.exceptions.AttrsAttributeNotFoundError">
<em class="property">exception </em><code class="descclassname">attr.exceptions.</code><code class="descname">AttrsAttributeNotFoundError</code><a class="headerlink" href="#attr.exceptions.AttrsAttributeNotFoundError" title="Permalink to this definition">¶</a></dt>
<dd><p>An <code class="docutils literal"><span class="pre">attrs</span></code> function couldn’t find an attribute that the user asked for.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.2.0.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="attr.exceptions.NotAnAttrsClassError">
<em class="property">exception </em><code class="descclassname">attr.exceptions.</code><code class="descname">NotAnAttrsClassError</code><a class="headerlink" href="#attr.exceptions.NotAnAttrsClassError" title="Permalink to this definition">¶</a></dt>
<dd><p>A non-<code class="docutils literal"><span class="pre">attrs</span></code> class has been passed into an <code class="docutils literal"><span class="pre">attrs</span></code> function.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.2.0.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="attr.exceptions.DefaultAlreadySetError">
<em class="property">exception </em><code class="descclassname">attr.exceptions.</code><code class="descname">DefaultAlreadySetError</code><a class="headerlink" href="#attr.exceptions.DefaultAlreadySetError" title="Permalink to this definition">¶</a></dt>
<dd><p>A default has been set using <code class="docutils literal"><span class="pre">attr.ib()</span></code> and is attempted to be reset
using the decorator.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0.</span></p>
</div>
</dd></dl>
<dl class="exception">
<dt id="attr.exceptions.UnannotatedAttributeError">
<em class="property">exception </em><code class="descclassname">attr.exceptions.</code><code class="descname">UnannotatedAttributeError</code><a class="headerlink" href="#attr.exceptions.UnannotatedAttributeError" title="Permalink to this definition">¶</a></dt>
<dd><p>A class with <code class="docutils literal"><span class="pre">auto_attribs=True</span></code> has an <code class="docutils literal"><span class="pre">attr.ib()</span></code> without a type
annotation.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.3.0.</span></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span><span class="p">(</span><span class="n">auto_attribs</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">C</span><span class="p">:</span>
<span class="n">x</span><span class="p">:</span> <span class="nb">int</span>
<span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
</pre></div>
</div>
</dd></dl>
<div class="section" id="influencing-initialization">
<h3>Influencing Initialization<a class="headerlink" href="#influencing-initialization" title="Permalink to this headline">¶</a></h3>
<p>Generally speaking, it’s best to keep logic out of your <code class="docutils literal"><span class="pre">__init__</span></code>.
The moment you need a finer control over how your class is instantiated, it’s usually best to use a classmethod factory or to apply the <a class="reference external" href="https://en.wikipedia.org/wiki/Builder_pattern">builder pattern</a>.</p>
<p>However, sometimes you need to do that one quick thing after your class is initialized.
And for that <code class="docutils literal"><span class="pre">attrs</span></code> offers the <code class="docutils literal"><span class="pre">__attrs_post_init__</span></code> hook that is automatically detected and run after <code class="docutils literal"><span class="pre">attrs</span></code> is done initializing your instance:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">init</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__attrs_post_init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">y</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">x</span> <span class="o">+</span> <span class="mi">1</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">C(x=1, y=2)</span>
</pre></div>
</div>
<p>Please note that you can’t directly set attributes on frozen classes:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span><span class="p">(</span><span class="n">frozen</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">FrozenBroken</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">init</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__attrs_post_init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">y</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">x</span> <span class="o">+</span> <span class="mi">1</span>
<span class="gp">>>> </span><span class="n">FrozenBroken</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">attr.exceptions.FrozenInstanceError</span>: <span class="n">can't set attribute</span>
</pre></div>
</div>
<p>If you need to set attributes on a frozen class, you’ll have to resort to the <a class="reference internal" href="how-does-it-work.html#how-frozen"><span class="std std-ref">same trick</span></a> as <code class="docutils literal"><span class="pre">attrs</span></code> and use <a class="reference external" href="/usr/share/doc/python3-doc/html/reference/datamodel.html#object.__setattr__" title="(in Python v3.6)"><code class="xref py py-meth docutils literal"><span class="pre">object.__setattr__()</span></code></a>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span><span class="p">(</span><span class="n">frozen</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">Frozen</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">init</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__attrs_post_init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">object</span><span class="o">.</span><span class="fm">__setattr__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="s2">"y"</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">x</span> <span class="o">+</span> <span class="mi">1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">Frozen</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">Frozen(x=1, y=2)</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="helpers">
<span id="id2"></span><h2>Helpers<a class="headerlink" href="#helpers" title="Permalink to this headline">¶</a></h2>
<p><code class="docutils literal"><span class="pre">attrs</span></code> comes with a bunch of helper methods that make working with it easier:</p>
<dl class="function">
<dt id="attr.fields">
<code class="descclassname">attr.</code><code class="descname">fields</code><span class="sig-paren">(</span><em>cls</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.fields" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns the tuple of <code class="docutils literal"><span class="pre">attrs</span></code> attributes for a class.</p>
<p>The tuple also allows accessing the fields by their names (see below for
examples).</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><p class="first"><strong>cls</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#type" title="(in Python v3.6)"><em>type</em></a>) – Class to introspect.</p>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><ul class="first simple">
<li><a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><strong>TypeError</strong></a> – If <em>cls</em> is not a class.</li>
<li><a class="reference internal" href="#attr.exceptions.NotAnAttrsClassError" title="attr.exceptions.NotAnAttrsClassError"><strong>attr.exceptions.NotAnAttrsClassError</strong></a> – If <em>cls</em> is not an <code class="docutils literal"><span class="pre">attrs</span></code>
class.</li>
</ul>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><p class="first last">tuple (with name accessors) of <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a></p>
</td>
</tr>
</tbody>
</table>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 16.2.0: </span>Returned tuple allows accessing the fields
by name.</p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">C</span><span class="p">)</span>
<span class="go">(Attribute(name='x', default=NOTHING, validator=None, repr=True, cmp=True, hash=None, init=True, metadata=mappingproxy({}), type=None, converter=None), Attribute(name='y', default=NOTHING, validator=None, repr=True, cmp=True, hash=None, init=True, metadata=mappingproxy({}), type=None, converter=None))</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">C</span><span class="p">)[</span><span class="mi">1</span><span class="p">]</span>
<span class="go">Attribute(name='y', default=NOTHING, validator=None, repr=True, cmp=True, hash=None, init=True, metadata=mappingproxy({}), type=None, converter=None)</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">C</span><span class="p">)</span><span class="o">.</span><span class="n">y</span> <span class="ow">is</span> <span class="n">attr</span><span class="o">.</span><span class="n">fields</span><span class="p">(</span><span class="n">C</span><span class="p">)[</span><span class="mi">1</span><span class="p">]</span>
<span class="go">True</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.has">
<code class="descclassname">attr.</code><code class="descname">has</code><span class="sig-paren">(</span><em>cls</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.has" title="Permalink to this definition">¶</a></dt>
<dd><p>Check whether <em>cls</em> is a class with <code class="docutils literal"><span class="pre">attrs</span></code> attributes.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>cls</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#type" title="(in Python v3.6)"><em>type</em></a>) – Class to introspect.</td>
</tr>
<tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><strong>TypeError</strong></a> – If <em>cls</em> is not a class.</td>
</tr>
<tr class="field-odd field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">bool</span></code></a></td>
</tr>
</tbody>
</table>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">has</span><span class="p">(</span><span class="n">C</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">has</span><span class="p">(</span><span class="nb">object</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.asdict">
<code class="descclassname">attr.</code><code class="descname">asdict</code><span class="sig-paren">(</span><em>inst</em>, <em>recurse=True</em>, <em>filter=None</em>, <em>dict_factory=<class 'dict'></em>, <em>retain_collection_types=False</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.asdict" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the <code class="docutils literal"><span class="pre">attrs</span></code> attribute values of <em>inst</em> as a dict.</p>
<p>Optionally recurse into other <code class="docutils literal"><span class="pre">attrs</span></code>-decorated classes.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>inst</strong> – Instance of an <code class="docutils literal"><span class="pre">attrs</span></code>-decorated class.</li>
<li><strong>recurse</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Recurse into classes that are also
<code class="docutils literal"><span class="pre">attrs</span></code>-decorated.</li>
<li><strong>filter</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – A callable whose return code determines whether an
attribute or element is included (<code class="docutils literal"><span class="pre">True</span></code>) or dropped (<code class="docutils literal"><span class="pre">False</span></code>). Is
called with the <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a> as the first argument and the
value as the second argument.</li>
<li><strong>dict_factory</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – A callable to produce dictionaries from. For
example, to produce ordered dictionaries instead of normal Python
dictionaries, pass in <code class="docutils literal"><span class="pre">collections.OrderedDict</span></code>.</li>
<li><strong>retain_collection_types</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Do not convert to <code class="docutils literal"><span class="pre">list</span></code> when
encountering an attribute whose type is <code class="docutils literal"><span class="pre">tuple</span></code> or <code class="docutils literal"><span class="pre">set</span></code>. Only
meaningful if <code class="docutils literal"><span class="pre">recurse</span></code> is <code class="docutils literal"><span class="pre">True</span></code>.</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">return type of <em>dict_factory</em></p>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Raises:</th><td class="field-body"><p class="first last"><a class="reference internal" href="#attr.exceptions.NotAnAttrsClassError" title="attr.exceptions.NotAnAttrsClassError"><strong>attr.exceptions.NotAnAttrsClassError</strong></a> – If <em>cls</em> is not an <code class="docutils literal"><span class="pre">attrs</span></code>
class.</p>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.0.0: </span><em>dict_factory</em></p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.1.0: </span><em>retain_collection_types</em></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">asdict</span><span class="p">(</span><span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">C</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">)))</span>
<span class="go">{'x': 1, 'y': {'x': 2, 'y': 3}}</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.astuple">
<code class="descclassname">attr.</code><code class="descname">astuple</code><span class="sig-paren">(</span><em>inst</em>, <em>recurse=True</em>, <em>filter=None</em>, <em>tuple_factory=<class 'tuple'></em>, <em>retain_collection_types=False</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.astuple" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the <code class="docutils literal"><span class="pre">attrs</span></code> attribute values of <em>inst</em> as a tuple.</p>
<p>Optionally recurse into other <code class="docutils literal"><span class="pre">attrs</span></code>-decorated classes.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>inst</strong> – Instance of an <code class="docutils literal"><span class="pre">attrs</span></code>-decorated class.</li>
<li><strong>recurse</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Recurse into classes that are also
<code class="docutils literal"><span class="pre">attrs</span></code>-decorated.</li>
<li><strong>filter</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – A callable whose return code determines whether an
attribute or element is included (<code class="docutils literal"><span class="pre">True</span></code>) or dropped (<code class="docutils literal"><span class="pre">False</span></code>). Is
called with the <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a> as the first argument and the
value as the second argument.</li>
<li><strong>tuple_factory</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – A callable to produce tuples from. For
example, to produce lists instead of tuples.</li>
<li><strong>retain_collection_types</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#bool" title="(in Python v3.6)"><em>bool</em></a>) – Do not convert to <code class="docutils literal"><span class="pre">list</span></code>
or <code class="docutils literal"><span class="pre">dict</span></code> when encountering an attribute which type is
<code class="docutils literal"><span class="pre">tuple</span></code>, <code class="docutils literal"><span class="pre">dict</span></code> or <code class="docutils literal"><span class="pre">set</span></code>. Only meaningful if <code class="docutils literal"><span class="pre">recurse</span></code> is
<code class="docutils literal"><span class="pre">True</span></code>.</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">return type of <em>tuple_factory</em></p>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Raises:</th><td class="field-body"><p class="first last"><a class="reference internal" href="#attr.exceptions.NotAnAttrsClassError" title="attr.exceptions.NotAnAttrsClassError"><strong>attr.exceptions.NotAnAttrsClassError</strong></a> – If <em>cls</em> is not an <code class="docutils literal"><span class="pre">attrs</span></code>
class.</p>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 16.2.0.</span></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">astuple</span><span class="p">(</span><span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">))</span>
<span class="go">(1, 2)</span>
</pre></div>
</div>
</dd></dl>
<p><code class="docutils literal"><span class="pre">attrs</span></code> includes some handy helpers for filtering:</p>
<dl class="function">
<dt id="attr.filters.include">
<code class="descclassname">attr.filters.</code><code class="descname">include</code><span class="sig-paren">(</span><em>*what</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.filters.include" title="Permalink to this definition">¶</a></dt>
<dd><p>Whitelist <em>what</em>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>what</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#list" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">list</span></code></a> of <a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#type" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">type</span></code></a> or <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a>s) – What to whitelist.</td>
</tr>
<tr class="field-even field"><th class="field-name">Return type:</th><td class="field-body"><code class="xref py py-class docutils literal"><span class="pre">callable</span></code></td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="attr.filters.exclude">
<code class="descclassname">attr.filters.</code><code class="descname">exclude</code><span class="sig-paren">(</span><em>*what</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.filters.exclude" title="Permalink to this definition">¶</a></dt>
<dd><p>Blacklist <em>what</em>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>what</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#list" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">list</span></code></a> of classes or <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a>s.) – What to blacklist.</td>
</tr>
<tr class="field-even field"><th class="field-name">Return type:</th><td class="field-body"><code class="xref py py-class docutils literal"><span class="pre">callable</span></code></td>
</tr>
</tbody>
</table>
</dd></dl>
<p>See <a class="reference internal" href="examples.html#asdict"><span class="std std-ref">Converting to Collections Types</span></a> for examples.</p>
<dl class="function">
<dt id="attr.evolve">
<code class="descclassname">attr.</code><code class="descname">evolve</code><span class="sig-paren">(</span><em>inst</em>, <em>**changes</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.evolve" title="Permalink to this definition">¶</a></dt>
<dd><p>Create a new instance, based on <em>inst</em> with <em>changes</em> applied.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>inst</strong> – Instance of a class with <code class="docutils literal"><span class="pre">attrs</span></code> attributes.</li>
<li><strong>changes</strong> – Keyword changes in the new copy.</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A copy of inst with <em>changes</em> incorporated.</p>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Raises:</th><td class="field-body"><ul class="first last simple">
<li><a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><strong>TypeError</strong></a> – If <em>attr_name</em> couldn’t be found in the class
<code class="docutils literal"><span class="pre">__init__</span></code>.</li>
<li><a class="reference internal" href="#attr.exceptions.NotAnAttrsClassError" title="attr.exceptions.NotAnAttrsClassError"><strong>attr.exceptions.NotAnAttrsClassError</strong></a> – If <em>cls</em> is not an <code class="docutils literal"><span class="pre">attrs</span></code>
class.</li>
</ul>
</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0.</span></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">y</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">i1</span> <span class="o">=</span> <span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">i1</span>
<span class="go">C(x=1, y=2)</span>
<span class="gp">>>> </span><span class="n">i2</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">evolve</span><span class="p">(</span><span class="n">i1</span><span class="p">,</span> <span class="n">y</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">i2</span>
<span class="go">C(x=1, y=3)</span>
<span class="gp">>>> </span><span class="n">i1</span> <span class="o">==</span> <span class="n">i2</span>
<span class="go">False</span>
</pre></div>
</div>
<p><code class="docutils literal"><span class="pre">evolve</span></code> creates a new instance using <code class="docutils literal"><span class="pre">__init__</span></code>.
This fact has several implications:</p>
<ul class="simple">
<li>private attributes should be specified without the leading underscore, just like in <code class="docutils literal"><span class="pre">__init__</span></code>.</li>
<li>attributes with <code class="docutils literal"><span class="pre">init=False</span></code> can’t be set with <code class="docutils literal"><span class="pre">evolve</span></code>.</li>
<li>the usual <code class="docutils literal"><span class="pre">__init__</span></code> validators will validate the new values.</li>
</ul>
</dd></dl>
<dl class="function">
<dt id="attr.validate">
<code class="descclassname">attr.</code><code class="descname">validate</code><span class="sig-paren">(</span><em>inst</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.validate" title="Permalink to this definition">¶</a></dt>
<dd><p>Validate all attributes on <em>inst</em> that have a validator.</p>
<p>Leaves all exceptions through.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>inst</strong> – Instance of a class with <code class="docutils literal"><span class="pre">attrs</span></code> attributes.</td>
</tr>
</tbody>
</table>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">instance_of</span><span class="p">(</span><span class="nb">int</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">i</span> <span class="o">=</span> <span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">i</span><span class="o">.</span><span class="n">x</span> <span class="o">=</span> <span class="s2">"1"</span>
<span class="gp">>>> </span><span class="n">attr</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">i</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">("'x' must be <type 'int'> (got '1' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, repr=True, cmp=True, hash=None, init=True, type=None), <type 'int'>, '1')</span>
</pre></div>
</div>
</dd></dl>
<p>Validators can be globally disabled if you want to run them only in development and tests but not in production because you fear their performance impact:</p>
<dl class="function">
<dt id="attr.set_run_validators">
<code class="descclassname">attr.</code><code class="descname">set_run_validators</code><span class="sig-paren">(</span><em>run</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.set_run_validators" title="Permalink to this definition">¶</a></dt>
<dd><p>Set whether or not validators are run. By default, they are run.</p>
</dd></dl>
<dl class="function">
<dt id="attr.get_run_validators">
<code class="descclassname">attr.</code><code class="descname">get_run_validators</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#attr.get_run_validators" title="Permalink to this definition">¶</a></dt>
<dd><p>Return whether or not validators are run.</p>
</dd></dl>
</div>
<div class="section" id="validators">
<span id="api-validators"></span><h2>Validators<a class="headerlink" href="#validators" title="Permalink to this headline">¶</a></h2>
<p><code class="docutils literal"><span class="pre">attrs</span></code> comes with some common validators in the <code class="docutils literal"><span class="pre">attrs.validators</span></code> module:</p>
<dl class="function">
<dt id="attr.validators.instance_of">
<code class="descclassname">attr.validators.</code><code class="descname">instance_of</code><span class="sig-paren">(</span><em>type</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.validators.instance_of" title="Permalink to this definition">¶</a></dt>
<dd><p>A validator that raises a <a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a> if the initializer is called
with a wrong type for this particular attribute (checks are performed using
<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#isinstance" title="(in Python v3.6)"><code class="xref py py-func docutils literal"><span class="pre">isinstance()</span></code></a> therefore it’s also valid to pass a tuple of types).</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>type</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#type" title="(in Python v3.6)"><em>type</em></a><em> or </em><em>tuple of types</em>) – The type to check for.</td>
</tr>
<tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><strong>TypeError</strong></a> – With a human readable error message, the attribute
(of type <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a>), the expected type, and the value it
got.</td>
</tr>
</tbody>
</table>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">instance_of</span><span class="p">(</span><span class="nb">int</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
<span class="go">C(x=42)</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="s2">"42"</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">("'x' must be <type 'int'> (got '42' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, type=None), <type 'int'>, '42')</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="kc">None</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">("'x' must be <type 'int'> (got None that is a <type 'NoneType'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, repr=True, cmp=True, hash=None, init=True, type=None), <type 'int'>, None)</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.validators.in_">
<code class="descclassname">attr.validators.</code><code class="descname">in_</code><span class="sig-paren">(</span><em>options</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.validators.in_" title="Permalink to this definition">¶</a></dt>
<dd><p>A validator that raises a <a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#ValueError" title="(in Python v3.6)"><code class="xref py py-exc docutils literal"><span class="pre">ValueError</span></code></a> if the initializer is called
with a value that does not belong in the options provided. The check is
performed using <code class="docutils literal"><span class="pre">value</span> <span class="pre">in</span> <span class="pre">options</span></code>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>options</strong> (list, tuple, <a class="reference external" href="/usr/share/doc/python3-doc/html/library/enum.html#enum.Enum" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">enum.Enum</span></code></a>, …) – Allowed options.</td>
</tr>
<tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#ValueError" title="(in Python v3.6)"><strong>ValueError</strong></a> – With a human readable error message, the attribute (of
type <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a>), the expected options, and the value it
got.</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0.</span></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">enum</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">State</span><span class="p">(</span><span class="n">enum</span><span class="o">.</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">ON</span> <span class="o">=</span> <span class="s2">"on"</span>
<span class="gp">... </span> <span class="n">OFF</span> <span class="o">=</span> <span class="s2">"off"</span>
<span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">state</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">in_</span><span class="p">(</span><span class="n">State</span><span class="p">))</span>
<span class="gp">... </span> <span class="n">val</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">in_</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]))</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="n">State</span><span class="o">.</span><span class="n">ON</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="go">C(state=<State.ON: 'on'>, val=1)</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="s2">"on"</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">'state' must be in <enum 'State'> (got 'on')</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="n">State</span><span class="o">.</span><span class="n">ON</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">'val' must be in [1, 2, 3] (got 4)</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.validators.provides">
<code class="descclassname">attr.validators.</code><code class="descname">provides</code><span class="sig-paren">(</span><em>interface</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.validators.provides" title="Permalink to this definition">¶</a></dt>
<dd><p>A validator that raises a <a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a> if the initializer is called
with an object that does not provide the requested <em>interface</em> (checks are
performed using <code class="docutils literal"><span class="pre">interface.providedBy(value)</span></code> (see <a class="reference external" href="https://zopeinterface.readthedocs.io/en/latest/">zope.interface</a>).</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>interface</strong> (<em>zope.interface.Interface</em>) – The interface to check for.</td>
</tr>
<tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><a class="reference external" href="/usr/share/doc/python3-doc/html/library/exceptions.html#TypeError" title="(in Python v3.6)"><strong>TypeError</strong></a> – With a human readable error message, the attribute
(of type <a class="reference internal" href="#attr.Attribute" title="attr.Attribute"><code class="xref py py-class docutils literal"><span class="pre">attr.Attribute</span></code></a>), the expected interface, and the
value it got.</td>
</tr>
</tbody>
</table>
</dd></dl>
<dl class="function">
<dt id="attr.validators.and_">
<code class="descclassname">attr.validators.</code><code class="descname">and_</code><span class="sig-paren">(</span><em>*validators</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.validators.and_" title="Permalink to this definition">¶</a></dt>
<dd><p>A validator that composes multiple validators into one.</p>
<p>When called on a value, it runs all wrapped validators.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>validators</strong> (<em>callables</em>) – Arbitrary number of validators.</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0.</span></p>
</div>
<p>For convenience, it’s also possible to pass a list to <a class="reference internal" href="#attr.ib" title="attr.ib"><code class="xref py py-func docutils literal"><span class="pre">attr.ib()</span></code></a>’s validator argument.</p>
<p>Thus the following two statements are equivalent:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">and_</span><span class="p">(</span><span class="n">v1</span><span class="p">,</span> <span class="n">v2</span><span class="p">,</span> <span class="n">v3</span><span class="p">))</span>
<span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="p">[</span><span class="n">v1</span><span class="p">,</span> <span class="n">v2</span><span class="p">,</span> <span class="n">v3</span><span class="p">])</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="attr.validators.optional">
<code class="descclassname">attr.validators.</code><code class="descname">optional</code><span class="sig-paren">(</span><em>validator</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.validators.optional" title="Permalink to this definition">¶</a></dt>
<dd><p>A validator that makes an attribute optional. An optional attribute is one
which can be set to <code class="docutils literal"><span class="pre">None</span></code> in addition to satisfying the requirements of
the sub-validator.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>validator</strong> (callable or <a class="reference external" href="/usr/share/doc/python3-doc/html/library/stdtypes.html#list" title="(in Python v3.6)"><code class="xref py py-class docutils literal"><span class="pre">list</span></code></a> of callables.) – A validator (or a list of validators) that is used for
non-<code class="docutils literal"><span class="pre">None</span></code> values.</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 15.1.0.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 17.1.0: </span><em>validator</em> can be a list of validators.</p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">validator</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">optional</span><span class="p">(</span><span class="n">attr</span><span class="o">.</span><span class="n">validators</span><span class="o">.</span><span class="n">instance_of</span><span class="p">(</span><span class="nb">int</span><span class="p">)))</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
<span class="go">C(x=42)</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="s2">"42"</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">("'x' must be <type 'int'> (got '42' that is a <type 'str'>).", Attribute(name='x', default=NOTHING, validator=<instance_of validator for type <type 'int'>>, type=None), <type 'int'>, '42')</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="kc">None</span><span class="p">)</span>
<span class="go">C(x=None)</span>
</pre></div>
</div>
</dd></dl>
</div>
<div class="section" id="converters">
<h2>Converters<a class="headerlink" href="#converters" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="attr.converters.optional">
<code class="descclassname">attr.converters.</code><code class="descname">optional</code><span class="sig-paren">(</span><em>converter</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.converters.optional" title="Permalink to this definition">¶</a></dt>
<dd><p>A converter that allows an attribute to be optional. An optional attribute
is one which can be set to <code class="docutils literal"><span class="pre">None</span></code>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>converter</strong> (<a class="reference external" href="/usr/share/doc/python3-doc/html/library/functions.html#callable" title="(in Python v3.6)"><em>callable</em></a>) – the converter that is used for non-<code class="docutils literal"><span class="pre">None</span></code>
values.</td>
</tr>
</tbody>
</table>
<div class="versionadded">
<p><span class="versionmodified">New in version 17.1.0.</span></p>
</div>
<p>For example:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@attr</span><span class="o">.</span><span class="n">s</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">x</span> <span class="o">=</span> <span class="n">attr</span><span class="o">.</span><span class="n">ib</span><span class="p">(</span><span class="n">converter</span><span class="o">=</span><span class="n">attr</span><span class="o">.</span><span class="n">converters</span><span class="o">.</span><span class="n">optional</span><span class="p">(</span><span class="nb">int</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="kc">None</span><span class="p">)</span>
<span class="go">C(x=None)</span>
<span class="gp">>>> </span><span class="n">C</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
<span class="go">C(x=42)</span>
</pre></div>
</div>
</dd></dl>
</div>
<div class="section" id="deprecated-apis">
<h2>Deprecated APIs<a class="headerlink" href="#deprecated-apis" title="Permalink to this headline">¶</a></h2>
<p>The serious business aliases used to be called <code class="docutils literal"><span class="pre">attr.attributes</span></code> and <code class="docutils literal"><span class="pre">attr.attr</span></code>.
There are no plans to remove them but they shouldn’t be used in new code.</p>
<dl class="function">
<dt id="attr.assoc">
<code class="descclassname">attr.</code><code class="descname">assoc</code><span class="sig-paren">(</span><em>inst</em>, <em>**changes</em><span class="sig-paren">)</span><a class="headerlink" href="#attr.assoc" title="Permalink to this definition">¶</a></dt>
<dd><p>Copy <em>inst</em> and apply <em>changes</em>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><strong>inst</strong> – Instance of a class with <code class="docutils literal"><span class="pre">attrs</span></code> attributes.</li>
<li><strong>changes</strong> – Keyword changes in the new copy.</li>
</ul>
</td>
</tr>
<tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body"><p class="first">A copy of inst with <em>changes</em> incorporated.</p>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">Raises:</th><td class="field-body"><ul class="first last simple">
<li><a class="reference internal" href="#attr.exceptions.AttrsAttributeNotFoundError" title="attr.exceptions.AttrsAttributeNotFoundError"><strong>attr.exceptions.AttrsAttributeNotFoundError</strong></a> – If <em>attr_name</em> couldn’t
be found on <em>cls</em>.</li>
<li><a class="reference internal" href="#attr.exceptions.NotAnAttrsClassError" title="attr.exceptions.NotAnAttrsClassError"><strong>attr.exceptions.NotAnAttrsClassError</strong></a> – If <em>cls</em> is not an <code class="docutils literal"><span class="pre">attrs</span></code>
class.</li>
</ul>
</td>
</tr>
</tbody>
</table>
<div class="deprecated">
<p><span class="versionmodified">Deprecated since version 17.1.0: </span>Use <a class="reference internal" href="#attr.evolve" title="attr.evolve"><code class="xref py py-func docutils literal"><span class="pre">evolve()</span></code></a> instead.</p>
</div>
</dd></dl>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<p class="logo"><a href="index.html">
<img class="logo" src="_static/attrs_logo.svg" alt="Logo"/>
</a></p>
<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">API Reference</a><ul>
<li><a class="reference internal" href="#core">Core</a><ul>
<li><a class="reference internal" href="#influencing-initialization">Influencing Initialization</a></li>
</ul>
</li>
<li><a class="reference internal" href="#helpers">Helpers</a></li>
<li><a class="reference internal" href="#validators">Validators</a></li>
<li><a class="reference internal" href="#converters">Converters</a></li>
<li><a class="reference internal" href="#deprecated-apis">Deprecated APIs</a></li>
</ul>
</li>
</ul>
<div class="relations">
<h3>Related Topics</h3>
<ul>
<li><a href="index.html">Documentation overview</a><ul>
<li>Previous: <a href="examples.html" title="previous chapter"><code class="docutils literal"><span class="pre">attrs</span></code> by Example</a></li>
<li>Next: <a href="extending.html" title="next chapter">Extending</a></li>
</ul></li>
</ul>
</div>
<div id="searchbox" style="display: none" role="search">
<h3>Quick search</h3>
<form class="search" action="search.html" method="get">
<div><input type="text" name="q" /></div>
<div><input type="submit" value="Go" /></div>
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('#searchbox').show(0);</script>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="footer">
©2018, Hynek Schlawack.
|
Powered by <a href="http://sphinx-doc.org/">Sphinx 1.6.7</a>
& <a href="https://github.com/bitprophet/alabaster">Alabaster 0.7.8</a>
</div>
</body>
</html>
|