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<div class="document" id="quixote-widget-classes">
<h1 class="title">Quixote Widget Classes</h1>
<p>[This is reference documentation. If you haven't yet read "Lesson 5:
widgets" of demo.txt, you should go and do so now. This document also
assumes you have a good understanding of HTML forms and form elements.
If not, you could do worse than pick up a copy of <em>HTML: The Definitive
Guide</em> by Chuck Musciano & Bill Kennedy (O'Reilly). I usually keep it
within arm's reach.]</p>
<p>Web forms are built out of form elements: string input, select lists,
checkboxes, submit buttons, and so forth. Quixote provides a family of
classes for handling these form elements, or widgets, in the
quixote.form.widget module. The class hierarchy is:</p>
<pre class="literal-block">
Widget [A]
|
+--StringWidget
| |
| +--PasswordWidget
| |
| +--NumberWidget [*] [A]
| |
| +-FloatWidget [*]
| +-IntWidget [*]
|
+--TextWidget
|
+--CheckboxWidget
|
+--SelectWidget [A]
| |
| +--SingleSelectWidget
| | |
| | +-RadiobuttonsWidget
| | |
| | +-OptionSelectWidget [*]
| |
| +--MultipleSelectWidget
|
+--SubmitButtonWidget
|
+--HiddenWidget
|
+--ListWidget [*]
[*] Widget classes that do not correspond exactly with a particular
HTML form element
[A] Abstract classes
</pre>
<div class="section" id="widget-the-base-class">
<h1><a name="widget-the-base-class">Widget: the base class</a></h1>
<p>Widget is the abstract base class for the widget hierarchy. It provides
the following facilities:</p>
<ul class="simple">
<li>widget name (<tt class="literal"><span class="pre">name</span></tt> attribute, <tt class="literal"><span class="pre">set_name()</span></tt> method)</li>
<li>widget value (<tt class="literal"><span class="pre">value</span></tt> attribute, <tt class="literal"><span class="pre">set_value()</span></tt> and <tt class="literal"><span class="pre">clear()</span></tt> methods)</li>
<li><tt class="literal"><span class="pre">__str__()</span></tt> and <tt class="literal"><span class="pre">__repr__()</span></tt> methods</li>
<li>some facilities for writing composite widget classes</li>
</ul>
<p>The Widget constructor signature is:</p>
<pre class="literal-block">
Widget(name : string, value : any = None)
</pre>
<dl>
<dt><tt class="literal"><span class="pre">name</span></tt></dt>
<dd>the name of the widget. For non-compound widgets (ie. everything in
the above class hierarchy), this will be used as the "name"
attribute for the main HTML tag that defines the form element.</dd>
<dt><tt class="literal"><span class="pre">value</span></tt></dt>
<dd>the current value of the form element. The type of 'value' depends
on the widget class. Most widget classes support only a single
type, eg. StringWidget always deals with strings and IntWidget with
integers. The SelectWidget classes are different; see the
descriptions below for details.</dd>
</dl>
</div>
<div class="section" id="common-widget-methods">
<h1><a name="common-widget-methods">Common widget methods</a></h1>
<p>The Widget base class also provides a couple of useful
methods:</p>
<dl>
<dt><tt class="literal"><span class="pre">set_name(name:string)</span></tt></dt>
<dd>use this to change the widget name supplied to the constructor.
Unless you know what you're doing, you should do this before
rendering or parsing the widget.</dd>
<dt><tt class="literal"><span class="pre">set_value(value:any)</span></tt></dt>
<dd>use this to set the widget value; this is the same as supplying
a value to the constructor (and the same type rules apply, ie.
the type of 'value' depends on the widget class).</dd>
<dt><tt class="literal"><span class="pre">clear()</span></tt></dt>
<dd>clear the widget's current value. Equivalent to
<tt class="literal"><span class="pre">widget.set_value(None)</span></tt>.</dd>
</dl>
<p>The following two methods will be used on every widget object you
create; if you write your own widget classes, you will almost certainly
have to define both of these:</p>
<dl>
<dt><tt class="literal"><span class="pre">render(request:HTTPRequest)</span></tt> <span class="classifier-delimiter">:</span> <span class="classifier"><tt class="literal"><span class="pre">string</span></tt></span></dt>
<dd>return a chunk of HTML that implements the form element
corresponding to this widget.</dd>
<dt><tt class="literal"><span class="pre">parse(request:HTTPRequest)</span></tt> <span class="classifier-delimiter">:</span> <span class="classifier"><tt class="literal"><span class="pre">any</span></tt></span></dt>
<dd>extract the form value for this widget from <tt class="literal"><span class="pre">request.form</span></tt>, parse it
according to the rules for this widget class, and return the
resulting value. The return value depends on the widget class, and
will be of the same type as the value passed to the constructor
and/or <tt class="literal"><span class="pre">set_value()</span></tt>.</dd>
</dl>
</div>
<div class="section" id="stringwidget">
<h1><a name="stringwidget">StringWidget</a></h1>
<p>Used for short, single-line string input with no validation (ie. any
string will be accepted.) Generates an <tt class="literal"><span class="pre"><input</span> <span class="pre">type="text"></span></tt> form
element.</p>
<div class="section" id="constructor">
<h2><a name="constructor">Constructor</a></h2>
<pre class="literal-block">
StringWidget(name : string,
value : string = None,
size : int = None,
maxlength : int = None)
</pre>
<dl>
<dt><tt class="literal"><span class="pre">size</span></tt></dt>
<dd>used as the <tt class="literal"><span class="pre">size</span></tt> attribute of the generated <tt class="literal"><span class="pre"><input></span></tt> tag;
controls the physical size of the input field.</dd>
<dt><tt class="literal"><span class="pre">maxlength</span></tt></dt>
<dd>used as the <tt class="literal"><span class="pre">maxlength</span></tt> attribute; controls the maximum amount
of input.</dd>
</dl>
</div>
<div class="section" id="examples">
<h2><a name="examples">Examples</a></h2>
<pre class="literal-block">
>>> StringWidget("foo", value="hello").render(request)
'<input name="foo" type="text" value="hello">'
>>> StringWidget("foo", size=10, maxlength=20).render(request)
'<input name="foo" type="text" size="10" maxlength="20">'
</pre>
</div>
</div>
<div class="section" id="passwordwidget">
<h1><a name="passwordwidget">PasswordWidget</a></h1>
<p>PasswordWidget is identical to StringWidget except for the type of the
HTML form element: <tt class="literal"><span class="pre">password</span></tt> instead of <tt class="literal"><span class="pre">text</span></tt>.</p>
</div>
<div class="section" id="textwidget">
<h1><a name="textwidget">TextWidget</a></h1>
<p>Used for multi-line text input. The value is a single string with
newlines right where the browser supplied them. (<tt class="literal"><span class="pre">\r\n</span></tt>, if present,
is converted to <tt class="literal"><span class="pre">\n</span></tt>.) Generates a <tt class="literal"><span class="pre"><textarea></span></tt> form element.</p>
<div class="section" id="id1">
<h2><a name="id1">Constructor</a></h2>
<pre class="literal-block">
TextWidget(name : string,
value : string = None,
cols : int = None,
rows : int = None,
wrap : string = "physical")
</pre>
<dl>
<dt><tt class="literal"><span class="pre">cols</span></tt>, <tt class="literal"><span class="pre">rows</span></tt></dt>
<dd>number of columns/rows in the textarea</dd>
<dt><tt class="literal"><span class="pre">wrap</span></tt></dt>
<dd>controls how the browser wraps text and includes newlines in the
submitted form value; consult an HTML book for details.</dd>
</dl>
</div>
</div>
<div class="section" id="checkboxwidget">
<h1><a name="checkboxwidget">CheckboxWidget</a></h1>
<p>Used for single boolean (on/off) value. The value you supply can be
anything, since Python has a boolean interpretation for all values; the
value returned by <tt class="literal"><span class="pre">parse()</span></tt> will always be 0 or 1 (but you shouldn't
rely on that!). Generates an <tt class="literal"><span class="pre"><input</span> <span class="pre">type="checkbox"></span></tt> form element.</p>
<div class="section" id="id2">
<h2><a name="id2">Constructor</a></h2>
<pre class="literal-block">
CheckboxWidget(name : string,
value : boolean = false)
</pre>
</div>
<div class="section" id="id3">
<h2><a name="id3">Examples</a></h2>
<pre class="literal-block">
>>> CheckboxWidget("foo", value=0).render(request)
'<input name="foo" type="checkbox" value="yes">'
>>> CheckboxWidget("foo", value="you bet").render(request)
'<input name="foo" type="checkbox" value="yes" checked>'
</pre>
</div>
</div>
<div class="section" id="radiobuttonswidget">
<h1><a name="radiobuttonswidget">RadiobuttonsWidget</a></h1>
<p>Used for a <em>set</em> of related radiobuttons, ie. several <tt class="literal"><span class="pre"><input</span>
<span class="pre">type="radio"></span></tt> tags with the same name and different values. The set
of values are supplied to the constructor as <tt class="literal"><span class="pre">allowed_values</span></tt>, which
may be a list of any Python objects (not just strings). The current
value must be either <tt class="literal"><span class="pre">None</span></tt> (the default) or one of the values in
<tt class="literal"><span class="pre">allowed_values</span></tt>; if you supply a <tt class="literal"><span class="pre">value</span></tt> not in <tt class="literal"><span class="pre">allowed_values</span></tt>,
it will be ignored. <tt class="literal"><span class="pre">parse()</span></tt> will return either <tt class="literal"><span class="pre">None</span></tt> or one of
the values in <tt class="literal"><span class="pre">allowed_values</span></tt>.</p>
<div class="section" id="id4">
<h2><a name="id4">Constructor</a></h2>
<pre class="literal-block">
RadiobuttonsWidget(name : string,
value : any = None,
allowed_values : [any] = None,
descriptions : [string] = map(str, allowed_values),
quote : boolean = true,
delim : string = "\n")
</pre>
<dl>
<dt><tt class="literal"><span class="pre">allowed_values</span></tt></dt>
<dd><p class="first">specifies how many <tt class="literal"><span class="pre"><input</span> <span class="pre">type="radio"></span></tt> tags to generate and the
values for each. Eg. <tt class="literal"><span class="pre">allowed_values=["foo",</span> <span class="pre">"bar"]</span></tt> will result in
(roughly):</p>
<pre class="last literal-block">
<input type="radio" value="foo">
<input type="radio" value="bar">
</pre>
</dd>
<dt><tt class="literal"><span class="pre">descriptions</span></tt></dt>
<dd>the text that will actually be shown to the user in the web page
that includes this widget. Handy when the elements of
<tt class="literal"><span class="pre">allowed_values</span></tt> are too terse, or don't have a meaningful
<tt class="literal"><span class="pre">str()</span></tt>, or you want to add some additional cues for the user. If
not supplied, <tt class="literal"><span class="pre">map(str,</span> <span class="pre">allowed_values)</span></tt> is used, with the
exception that <tt class="literal"><span class="pre">None</span></tt> in <tt class="literal"><span class="pre">allowed_values</span></tt> becomes <tt class="literal"><span class="pre">""</span></tt> (the
empty string) in <tt class="literal"><span class="pre">descriptions</span></tt>. If supplied, <tt class="literal"><span class="pre">descriptions</span></tt>
must be the same length as <tt class="literal"><span class="pre">allowed_values</span></tt>.</dd>
<dt><tt class="literal"><span class="pre">quote</span></tt></dt>
<dd>if true (the default), the elements of 'descriptions' will be
HTML-quoted (using <tt class="literal"><span class="pre">quixote.html.html_quote()</span></tt>) when the widget is
rendered. This is essential if you might have characters like
<tt class="literal"><span class="pre">&</span></tt> or <tt class="literal"><span class="pre"><</span></tt> in your descriptions. However, you'll want to set
<tt class="literal"><span class="pre">quote</span></tt> to false if you are deliberately including HTML markup
in your descriptions.</dd>
<dt><tt class="literal"><span class="pre">delim</span></tt></dt>
<dd>the delimiter to separate the radiobuttons with when rendering
the whole widget. The default ensures that your HTML is readable
(by putting each <tt class="literal"><span class="pre"><input></span></tt> tag on a separate line), and that there
is horizontal whitespace between each radiobutton.</dd>
</dl>
</div>
<div class="section" id="id5">
<h2><a name="id5">Examples</a></h2>
<pre class="literal-block">
>>> colours = ["red", "green", "blue", "pink"]
>>> widget = RadiobuttonsWidget("foo", allowed_values=colours)
>>> print widget.render(request)
<input name="foo" type="radio" value="0">red</input>
<input name="foo" type="radio" value="1">green</input>
<input name="foo" type="radio" value="2">blue</input>
<input name="foo" type="radio" value="3">pink</input>
</pre>
<p>(Note that the actual form values, ie. what the browser returns to the
server, are always stringified indices into the 'allowed_values' list.
This is irrelevant to you, since SingleSelectWidget takes care of
converting <tt class="literal"><span class="pre">"1"</span></tt> to <tt class="literal"><span class="pre">1</span></tt> and looking up <tt class="literal"><span class="pre">allowed_values[1]</span></tt>.)</p>
<pre class="literal-block">
>>> values = [val1, val2, val3]
>>> descs = ["thing <b>1</b>",
"thing <b>2</b>",
"thing <b>3</b>"]
>>> widget = RadiobuttonsWidget("bar",
allowed_values=values,
descriptions=descs,
value=val3,
delim="<br>\n",
quote=0)
>>> print widget.render(request)
<input name="bar" type="radio" value="0">thing <b>1</b></input><br>
<input name="bar" type="radio" value="1">thing <b>2</b></input><br>
<input name="bar" type="radio" value="2" checked="checked">thing <b>3</b></input>
</pre>
</div>
</div>
<div class="section" id="singleselectwidget">
<h1><a name="singleselectwidget">SingleSelectWidget</a></h1>
<p>Used to select a single value from a list that's too long or ungainly
for a set of radiobuttons. (Most browsers implement this as a scrolling
list; UNIX versions of Netscape 4.x and earlier used a pop-up menu.)
The value can be any Python object; <tt class="literal"><span class="pre">parse()</span></tt> will return either
<tt class="literal"><span class="pre">None</span></tt> or one of the values you supply to the constructor as
<tt class="literal"><span class="pre">allowed_values</span></tt>. Generates a <tt class="literal"><span class="pre"><select>...</select></span></tt> tag, with one
<tt class="literal"><span class="pre"><option></span></tt> tag for each element of <tt class="literal"><span class="pre">allowed_values</span></tt>.</p>
<div class="section" id="id6">
<h2><a name="id6">Constructor</a></h2>
<pre class="literal-block">
SingleSelectWidget(name : string,
value : any = None,
allowed_values : [any] = None,
descriptions : [string] = map(str, allowed_values),
quote : boolean = true,
size : int = None)
</pre>
<dl>
<dt><tt class="literal"><span class="pre">allowed_values</span></tt></dt>
<dd>determines the set of <tt class="literal"><span class="pre"><option></span></tt> tags that will go inside the
<tt class="literal"><span class="pre"><select></span></tt> tag; these can be any Python values (not just strings).
<tt class="literal"><span class="pre">parse()</span></tt> will return either one of the <tt class="literal"><span class="pre">allowed_values</span></tt> or <tt class="literal"><span class="pre">None</span></tt>.
If you supply a <tt class="literal"><span class="pre">value</span></tt> that is not in <tt class="literal"><span class="pre">allowed_values</span></tt>, it
will be ignored.</dd>
<dt><tt class="literal"><span class="pre">descriptions</span></tt></dt>
<dd>(same as RadiobuttonsWidget above)</dd>
<dt><tt class="literal"><span class="pre">quote</span></tt></dt>
<dd>(same as RadiobuttonsWidget above)</dd>
<dt><tt class="literal"><span class="pre">size</span></tt></dt>
<dd>corresponds to the <tt class="literal"><span class="pre">size</span></tt> attribute of the <tt class="literal"><span class="pre"><select></span></tt> tag: ask
the browser to show a select list with <tt class="literal"><span class="pre">size</span></tt> items visible.
Not always respected by the browser; consult an HTML book.</dd>
</dl>
</div>
<div class="section" id="id7">
<h2><a name="id7">Examples</a></h2>
<pre class="literal-block">
>>> widget = SingleSelectWidget("foo",
allowed_values=["abc", 123, 5.5])
>>> print widget.render(request)
<select name="foo">
<option value="0">abc
<option value="1">123
<option value="2">5.5
</select>
>>> widget = SingleSelectWidget("bar",
value=val2,
allowed_values=[val1, val2, val3],
descriptions=["foo", "bar", "foo & bar"],
size=3)
>>> print widget.render(request)
<select name="bar" size="3">
<option value="0">foo
<option selected value="1">bar
<option value="2">foo &amp; bar
</select>
</pre>
</div>
</div>
<div class="section" id="multipleselectwidget">
<h1><a name="multipleselectwidget">MultipleSelectWidget</a></h1>
<p>Used to select multiple values from a list. Everything is just like
SingleSelectWidget, except that <tt class="literal"><span class="pre">value</span></tt> can be a list of objects
selected from <tt class="literal"><span class="pre">allowed_values</span></tt> (in which case every object in <tt class="literal"><span class="pre">value</span></tt>
will initially be selected). Generates a <tt class="literal"><span class="pre"><select</span> <span class="pre">multiple>...</select></span></tt>
tag, with one <tt class="literal"><span class="pre"><option></span></tt> tag for each element of <tt class="literal"><span class="pre">allowed_values</span></tt>.</p>
<div class="section" id="id8">
<h2><a name="id8">Constructor</a></h2>
<pre class="literal-block">
MultipleSelectWidget(name : string,
value : any | [any] = None,
allowed_values : [any] = None,
descriptions : [string] = map(str, allowed_values),
quote : boolean = true,
size : int = None)
</pre>
</div>
</div>
<div class="section" id="submitbuttonwidget">
<h1><a name="submitbuttonwidget">SubmitButtonWidget</a></h1>
<p>Used for generating submit buttons. Note that HTML submit buttons are
rather weird, and Quixote preserves this weirdness -- the Widget classes
are meant to be a fairly thin wrapper around HTML form elements, after
all.</p>
<p>In particular, the widget value for a submit button controls two things:
what the user sees in their browser (the text in the button) and what
the browser returns as the value for that form element. You can't
control the two separately, as you can with radiobuttons or selection
widgets.</p>
<p>Also, SubmitButtonWidget is the only widget with an optional <tt class="literal"><span class="pre">name</span></tt>.
In many simple forms, all you care about is the fact that the form was
submitted -- which submit button the user used doesn't matter.</p>
<div class="section" id="id9">
<h2><a name="id9">Constructor</a></h2>
<pre class="literal-block">
SubmitButtonWidget(name : string = None,
value : string = None)
</pre>
<dl>
<dt><tt class="literal"><span class="pre">value</span></tt></dt>
<dd>the text that will be shown in the user's browser, <em>and</em> the
value that will be returned for this form element (widget)
if the user selects this submit button.</dd>
</dl>
</div>
<div class="section" id="id10">
<h2><a name="id10">Examples</a></h2>
<blockquote>
<pre class="doctest-block">
>>> SubmitButtonWidget(value="Submit Form").render(request)
'<input type="submit" value="Submit Form">'
</pre>
</blockquote>
</div>
</div>
<div class="section" id="hiddenwidget">
<h1><a name="hiddenwidget">HiddenWidget</a></h1>
<p>Used to generate HTML hidden widgets, which can be useful for carrying
around non-sensitive application state. (The Quixote form framework
uses hidden widgets for form tokens as a measure against cross-site
request forgery [CSRF] attacks. So by "sensitive" I mean "information
which should not be revealed", rather than "security-related". If you
wouldn't put it in a cookie or in email, don't put it in a hidden form
element.)</p>
<div class="section" id="id11">
<h2><a name="id11">Constructor</a></h2>
<pre class="literal-block">
HiddenWidget(name : string,
value : string)
</pre>
</div>
<div class="section" id="id12">
<h2><a name="id12">Examples</a></h2>
<pre class="literal-block">
>>> HiddenWidget("form_id", "2452345135").render(request)
'<input type="hidden" name="form_id" value="2452345135">'
</pre>
</div>
</div>
<div class="section" id="intwidget">
<h1><a name="intwidget">IntWidget</a></h1>
<p>The first derived widget class: this is a subclass of StringWidget
specifically for entering integer values. As such, this is the first
widget class we've covered that can reject certain user input. (The
selection widgets all have to validate their input in case of broken or
malicious clients, but they just drop bogus values.) If the user enters
a string that Python's built-in <tt class="literal"><span class="pre">int()</span></tt> can't convert to an integer,
IntWidget's <tt class="literal"><span class="pre">parse()</span></tt> method raises FormValueError (also defined in
the quixote.form.widget module). This exception is handled by Quixote's
form framework, but if you're using widget objects on their own, you'll
have to handle it yourself.</p>
<p><tt class="literal"><span class="pre">IntWidget.parse()</span></tt> always returns an integer or <tt class="literal"><span class="pre">None</span></tt>.</p>
<div class="section" id="id13">
<h2><a name="id13">Constructor</a></h2>
<pre class="literal-block">
IntWidget(name : string,
value : int = None,
size : int = None,
maxlength : int = None)
</pre>
<p>Constructor arguments are as for StringWidget, except that <tt class="literal"><span class="pre">value</span></tt>
must be an integer (or <tt class="literal"><span class="pre">None</span></tt>). Note that <tt class="literal"><span class="pre">size</span></tt> and
<tt class="literal"><span class="pre">maxlength</span></tt> have exactly the same meaning: they control the size of
the input widget and the maximum number of characters of input.</p>
<p>[Examples]</p>
<blockquote>
<pre class="doctest-block">
>>> IntWidget("num", value=37, size=5).render(request)
'<input type="string" name="num" value="37" size="5">'
</pre>
</blockquote>
</div>
</div>
<div class="section" id="floatwidget">
<h1><a name="floatwidget">FloatWidget</a></h1>
<p>FloatWidget is identical to IntWidget, except:</p>
<ul class="simple">
<li><tt class="literal"><span class="pre">value</span></tt> must be a float</li>
<li><tt class="literal"><span class="pre">parse()</span></tt> returns a float or <tt class="literal"><span class="pre">None</span></tt></li>
<li><tt class="literal"><span class="pre">parse()</span></tt> raises FormValueError if the string entered by the
user cannot be converted by Python's built-in <tt class="literal"><span class="pre">float()</span></tt> function</li>
</ul>
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<div class="section" id="optionselectwidget">
<h1><a name="optionselectwidget">OptionSelectWidget</a></h1>
<p>OptionSelectWidget is simply a SingleSelectWidget that uses a bit of
Javascript to automatically submit the current form as soon as the user
selects a value. This is useful for very simple one-element forms where
you don't want to bother with a submit button, or for very complex forms
where you need to revamp the user interface based on a user's selection.
Your form-processing code could then detect that style of form
submission, and regenerate a slightly different form for the user. (Or
you could treat it as a full-blown form submission, if the only widget
of interest is the OptionSelectWidget.)</p>
<p>For example, if you're asking a user for their address, some of the
details will vary depending on which country they're in. You might make
the country widget an OptionSelectWidget: if the user selects "Canada",
you'll ask them for a province and a postal code; if they select "United
States", you ask for a state and a zip code; and so forth. (I don't
really recommend a user interface that works this way: you'll spend way
too much time getting the details right ["How many states does Australia
have again?"], and you're bound to get something wrong -- there are over
200 countries in the world, after all.)</p>
<p>Be warned that since OptionSelectWidget relies on Javascript to work,
using it makes immediately makes your application less portable and more
fragile. One thing to avoid: form elements with a name of <tt class="literal"><span class="pre">submit</span></tt>,
since that masks the Javascript function called by OptionSelectWidget.</p>
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