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<div class="section" id="user-manual">
<h1>User Manual<a class="headerlink" href="#user-manual" title="Permalink to this headline">¶</a></h1>
<div class="section" id="quick-start">
<span id="index-0"></span><h2>Quick start<a class="headerlink" href="#quick-start" title="Permalink to this headline">¶</a></h2>
<p><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> provides <a class="reference external" href="https://www.python.org">Python</a> bindings for the ENVISAT Product Reader C API
(<a class="reference external" href="https://github.com/bcdev/epr-api">EPR API</a>) for reading satellite data from <a class="reference external" href="https://envisat.esa.int">ENVISAT</a> <a class="reference external" href="https://earth.esa.int">ESA</a> (European
Space Agency) mission.</p>
<p><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a>, as well as the <a class="reference external" href="https://github.com/bcdev/epr-api">EPR API</a> for C, supports <a class="reference external" href="https://envisat.esa.int">ENVISAT</a> MERIS, AATSR
Level 1B and Level 2 and also ASAR data products. It provides access to
the data either on a geophysical (decoded, ready-to-use pixel samples)
or on a raw data layer. The raw data access makes it possible to read
any data field contained in a product file.</p>
<p>Full access to the Python EPR API is provided by the <a class="reference internal" href="reference.html#module-epr" title="epr: Python bindings for ENVISAT Product Reader C API"><code class="xref py py-mod docutils literal"><span class="pre">epr</span></code></a> module that
have to be imported by the client program e.g. as follows:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">epr</span>
</pre></div>
</div>
<p>The following snippet open an ASAR product and dumps the “Main Processing
Parameters” record to the standard output:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">epr</span>
<span class="n">product</span> <span class="o">=</span> <span class="n">epr</span><span class="o">.</span><span class="n">Product</span><span class="p">(</span>
<span class="s1">'ASA_IMP_1PNUPA20060202_062233_000000152044_00435_20529_3110.N1'</span><span class="p">)</span>
<span class="n">dataset</span> <span class="o">=</span> <span class="n">product</span><span class="o">.</span><span class="n">get_dataset</span><span class="p">(</span><span class="s1">'MAIN_PROCESSING_PARAMS_ADS'</span><span class="p">)</span>
<span class="n">record</span> <span class="o">=</span> <span class="n">dataset</span><span class="o">.</span><span class="n">read_record</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="n">record</span><span class="p">)</span>
<span class="n">product</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Since version 0.9 <a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> also include <em>update</em> features that are not
available in the EPR C API.
The user can open a product in update mode (‘rb+’) and call the
<a class="reference internal" href="reference.html#epr.Field.set_elem" title="epr.Field.set_elem"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.set_elem()</span></code></a> and <a class="reference internal" href="reference.html#epr.Field.set_elems" title="epr.Field.set_elems"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.set_elems()</span></code></a> methods of
<a class="reference internal" href="reference.html#epr.Field" title="epr.Field"><code class="xref py py-class docutils literal"><span class="pre">epr.Field</span></code></a> class to update its elements and write changes to disk.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><a class="reference internal" href="#update-support">Update support</a> and <a class="reference internal" href="update_example.html"><span class="doc">Update Field elements</span></a> tutorial for details.</p>
</div>
</div>
<div class="section" id="requirements">
<span id="index-2"></span><h2>Requirements<a class="headerlink" href="#requirements" title="Permalink to this headline">¶</a></h2>
<p>In order to use PyEPR it is needed that the following software are
correctly installed and configured:</p>
<ul class="simple">
<li><a class="reference external" href="https://www.python.org">Python2</a> >= 2.6 or <a class="reference external" href="https://www.python.org">Python3</a> >= 3.1</li>
<li><a class="reference external" href="http://www.numpy.org">numpy</a> >= 1.5.0</li>
<li><a class="reference external" href="https://github.com/bcdev/epr-api">EPR API</a> >= 2.2 (optional, since PyEPR 0.7 the source tar-ball comes
with a copy of the PER C API sources)</li>
<li>a reasonably updated C compiler <a class="footnote-reference" href="#id3" id="id1">[1]</a> (build only)</li>
<li><a class="reference external" href="http://cython.org">Cython</a> >= 0.19 <a class="footnote-reference" href="#id4" id="id2">[2]</a> (optional and build only)</li>
<li><a class="reference external" href="https://pypi.python.org/pypi/unittest2">unittest2</a> (only required for Python < 2.7)</li>
</ul>
<table class="docutils footnote" frame="void" id="id3" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> has been developed and tested with <a class="reference external" href="http://gcc.gnu.org">gcc</a> 4.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id4" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id2">[2]</a></td><td><p class="first">The source tarball of official releases also includes the C extension
code generated by <a class="reference external" href="http://cython.org">cython</a> so users don’t strictly need <a class="reference external" href="http://cython.org">cython</a> to
install <a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a>.</p>
<p class="last">It is only needed to re-generate the C extension code (e.g. if one
wants to build a development version of <a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a>).</p>
</td></tr>
</tbody>
</table>
</div>
<div class="section" id="download">
<span id="index-3"></span><h2>Download<a class="headerlink" href="#download" title="Permalink to this headline">¶</a></h2>
<p>Official source tar-balls can be downloaded form <a class="reference external" href="https://pypi.python.org/pypi">PyPi</a>:</p>
<blockquote>
<div><a class="reference external" href="https://pypi.python.org/pypi/pyepr">https://pypi.python.org/pypi/pyepr</a></div></blockquote>
<p>The source code of the development versions is available on the <a class="reference external" href="https://github.com">GitHub</a>
project page</p>
<blockquote>
<div><a class="reference external" href="https://github.com/avalentino/pyepr">https://github.com/avalentino/pyepr</a></div></blockquote>
<p>To clone the <a class="reference external" href="http://git-scm.com">git</a> repository the following command can be used:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ git clone https://github.com/avalentino/pyepr.git
</pre></div>
</div>
</div>
<div class="section" id="installation">
<span id="index-4"></span><span id="id5"></span><h2>Installation<a class="headerlink" href="#installation" title="Permalink to this headline">¶</a></h2>
<p>The easier way to install <a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> is using tools like <a class="reference external" href="https://pypi.python.org/pypi/pip">pip</a>:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ pip install pyepr
</pre></div>
</div>
<p>For a user specific installation please use:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ pip install --user pyepr
</pre></div>
</div>
<p>To install <a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> in a non-standard path:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ pip install --install-option<span class="o">=</span><span class="s2">"--prefix=<TARGET_PATH>"</span> pyepr
</pre></div>
</div>
<p>just make sure that <code class="file docutils literal"><span class="pre"><TARGET_PATH>/lib/pythonX.Y/site-packages</span></code> is in
the <span class="target" id="index-5"></span><a class="reference external" href="https://docs.python.org/3/using/cmdline.html#envvar-PYTHONPATH" title="(in Python v3.6)"><code class="xref std std-envvar docutils literal"><span class="pre">PYTHONPATH</span></code></a>.</p>
<p id="index-6"><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> can be installed from sources using the following command:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ python setup.py install
</pre></div>
</div>
<p>The <code class="file docutils literal"><span class="pre">setup.py</span></code> script by default checks for the availability of the
EPR C API source code in the <code class="file docutils literal"><span class="pre"><package-root>/epr-api-src</span></code> directory
and tries to build PyEPR in <em>standalone mode</em>, i.e. without linking an
external dynamic library of EPR-API.</p>
<p>If no EPR C API sources are found then the <code class="file docutils literal"><span class="pre">setup.py</span></code> script
automatically tries to link the EPR-API dynamic library.
This can happen, for example, if the user is using a copy of the PyEPR
sources cloned from a <a class="reference external" href="http://git-scm.com">git</a> repository.
In this case it is assumed that the <a class="reference external" href="https://github.com/bcdev/epr-api">EPR API</a> C library is properly
installed in the system (see the <a class="reference internal" href="#requirements">Requirements</a> section).</p>
<p>It is possible to control which <a class="reference external" href="https://github.com/bcdev/epr-api">EPR API</a> C sources to use by means of the
<code class="xref std std-option docutils literal"><span class="pre">--epr-api-src</span></code> option of the <code class="file docutils literal"><span class="pre">setup.py</span></code> script:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ python setup.py install --epr-api-src<span class="o">=</span>../epr-api/src
</pre></div>
</div>
<p>Also it is possible to switch off the <em>standalone mode</em> and force the link
with the system <a class="reference external" href="https://github.com/bcdev/epr-api">EPR API</a> C library:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ python setup.py install --epr-api-src<span class="o">=</span>None
</pre></div>
</div>
</div>
<div class="section" id="testing">
<span id="index-7"></span><h2>Testing<a class="headerlink" href="#testing" title="Permalink to this headline">¶</a></h2>
<p><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> package comes with a complete test suite.
The test suite can be run using the following command in the <code class="file docutils literal"><span class="pre">tests</span></code>
directory:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ python test_all.py
</pre></div>
</div>
<p>or from the package root directory:</p>
<div class="highlight-sh"><div class="highlight"><pre><span></span>$ python setup.py <span class="nb">test</span>
</pre></div>
</div>
<p>The test script automatically downloads and decompresses the ENVISAT sample
product necessary for testing,
<a class="reference external" href="https://earth.esa.int/services/sample_products/meris/LRC/L2/MER_LRC_2PTGMV20000620_104318_00000104X000_00000_00000_0001.N1.gz">MER_LRC_2PTGMV20000620_104318_00000104X000_00000_00000_0001.N1</a>,
if it is not already available in the <code class="file docutils literal"><span class="pre">tests</span></code> directory.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>please note that, unless the user already have a copy of the specified
sample product correctly installed, an <strong>internet connection</strong> is
necessary the first time that the test suite is run.</p>
<p class="last">After the first run the sample product remains in the <code class="file docutils literal"><span class="pre">tests</span></code>
directory so the internet access is no longer necessary.</p>
</div>
</div>
<div class="section" id="python-vs-c-api">
<span id="index-8"></span><h2>Python vs C API<a class="headerlink" href="#python-vs-c-api" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference external" href="https://www.python.org">Python</a> EPR API is fully object oriented.
The main structures of the <a class="reference external" href="https://rawgithub.com/bcdev/epr-api/master/docs/epr_c_api/index.html">C API</a> have been implemented as objects while
C function have been logically grouped and mapped onto object methods.</p>
<p>The entire process of defining an object oriented API for <a class="reference external" href="https://www.python.org">Python</a> has
been quite easy and straightforward thanks to the good design of the C
API,</p>
<p>Of course there are also some differences that are illustrated in the
following sections.</p>
</div>
<div class="section" id="memory-management">
<span id="index-9"></span><h2>Memory management<a class="headerlink" href="#memory-management" title="Permalink to this headline">¶</a></h2>
<p>Being <a class="reference external" href="https://www.python.org">Python</a> a very high level language uses have never to worry about
memory allocation/de-allocation. They simply have to instantiate objects:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">product</span> <span class="o">=</span> <span class="n">epr</span><span class="o">.</span><span class="n">Product</span><span class="p">(</span><span class="s1">'filename.N1'</span><span class="p">)</span>
</pre></div>
</div>
<p>and use them freely.</p>
<p>Objects are automatically destroyed when there are no more references to
them and memory is de-allocated automatically.</p>
<p>Even better, each object holds a reference to other objects it depends
on so the user never have to worry about identifiers validity or about
the correct order structures have to be freed.</p>
<p>For example: the C <cite>EPR_DatasetId</cite> structure has a field (<cite>product_id</cite>)
that points to the <em>product</em> descriptor <cite>EPR_productId</cite> to which it
belongs to.</p>
<p id="index-10">The reference to the parent product is used, for example, when one wants
to read a record using the <cite>epr_read_record</cite> function:</p>
<div class="highlight-c"><div class="highlight"><pre><span></span><span class="n">EPR_SRecord</span><span class="o">*</span> <span class="nf">epr_read_record</span><span class="p">(</span><span class="n">EPR_SDatasetId</span><span class="o">*</span> <span class="n">dataset_id</span><span class="p">,</span> <span class="p">...);</span>
</pre></div>
</div>
<p>The function takes a <cite>EPR_SDatasetId</cite> as a parameter and assumes all
fields (including <code class="docutils literal"><span class="pre">dataset->product_id</span></code>) are valid.
It is responsibility of the programmer to keep all structures valid and
free them at the right moment and in the correct order.</p>
<p>This is the standard way to go in C but not in <a class="reference external" href="https://www.python.org">Python</a>.</p>
<p>In <a class="reference external" href="https://www.python.org">Python</a> all is by far simpler, and the user can get a <em>dateset</em>
object instance:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">dataset</span> <span class="o">=</span> <span class="n">product</span><span class="o">.</span><span class="n">get_dataset</span><span class="p">(</span><span class="s1">'MAIN_PROCESSING_PARAMS_ADS'</span><span class="p">)</span>
</pre></div>
</div>
<p>and then forget about the <em>product</em> instance it depends on.
Even if the <em>product</em> variable goes out of <span class="target" id="index-11"></span>scope and it is no more
directly accessible in the program the <em>dataset</em> object keeps staying valid
since it holds an internal reference to the <em>product</em> instance it depends on.</p>
<p>When <em>record</em> is destroyed automatically also the parent <a class="reference internal" href="reference.html#epr.Product" title="epr.Product"><code class="xref py py-class docutils literal"><span class="pre">epr.Product</span></code></a>
object is destroyed (assumed there is no other <span class="target" id="index-12"></span>reference to it).</p>
<p>The entire machinery is completely automatic and transparent to the user.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">of course when a <em>product</em> object is explicitly closed using the
<a class="reference internal" href="reference.html#epr.Product.close" title="epr.Product.close"><code class="xref py py-meth docutils literal"><span class="pre">epr.Product.close()</span></code></a> any I/O operation on it and on other objects
(bands, datasets, etc) associated to it is no more possible.</p>
<span class="target" id="index-13"></span></div>
</div>
<div class="section" id="arrays">
<span id="index-14"></span><h2>Arrays<a class="headerlink" href="#arrays" title="Permalink to this headline">¶</a></h2>
<p><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> uses <a class="reference external" href="http://www.numpy.org">numpy</a> in order to manage efficiently the potentially large
amount of data contained in <a class="reference external" href="https://envisat.esa.int">ENVISAT</a> products.</p>
<ul>
<li><p class="first"><a class="reference internal" href="reference.html#epr.Field.get_elems" title="epr.Field.get_elems"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.get_elems()</span></code></a> return an 1D array containing elements of
the field</p>
</li>
<li><p class="first">the <cite>Raster.data</cite> property is a 2D array exposes data contained in the
<a class="reference internal" href="reference.html#epr.Raster" title="epr.Raster"><code class="xref py py-class docutils literal"><span class="pre">epr.Raster</span></code></a> object in form of <a class="reference external" href="http://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.html#numpy.ndarray" title="(in NumPy v1.13)"><code class="xref py py-class docutils literal"><span class="pre">numpy.ndarray</span></code></a></p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p><a class="reference internal" href="reference.html#epr.Raster.data" title="epr.Raster.data"><code class="xref py py-attr docutils literal"><span class="pre">epr.Raster.data</span></code></a> directly exposes <a class="reference internal" href="reference.html#epr.Raster" title="epr.Raster"><code class="xref py py-class docutils literal"><span class="pre">epr.Raster</span></code></a>
i.e. shares the same memory buffer with <a class="reference internal" href="reference.html#epr.Raster" title="epr.Raster"><code class="xref py py-class docutils literal"><span class="pre">epr.Raster</span></code></a>:</p>
<div class="last highlight-python"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">raster</span><span class="o">.</span><span class="n">get_pixel</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">j</span><span class="p">)</span>
<span class="go">5</span>
<span class="gp">>>> </span><span class="n">raster</span><span class="o">.</span><span class="n">data</span><span class="p">[</span><span class="n">i</span><span class="p">,</span> <span class="n">j</span><span class="p">]</span>
<span class="go">5</span>
<span class="gp">>>> </span><span class="n">raster</span><span class="o">.</span><span class="n">data</span><span class="p">[</span><span class="n">i</span><span class="p">,</span> <span class="n">j</span><span class="p">]</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">>>> </span><span class="n">raster</span><span class="o">.</span><span class="n">get_pixel</span><span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">j</span><span class="p">)</span>
<span class="go">3</span>
</pre></div>
</div>
</div>
</li>
<li><p class="first"><a class="reference internal" href="reference.html#epr.Band.read_as_array" title="epr.Band.read_as_array"><code class="xref py py-meth docutils literal"><span class="pre">epr.Band.read_as_array()</span></code></a> is an additional method provided by
the <a class="reference external" href="https://www.python.org">Python</a> EPR API (does not exist any correspondent function in the
C API). It is mainly a facility method that allows users to get access
to band data without creating an intermediate <a class="reference internal" href="reference.html#epr.Raster" title="epr.Raster"><code class="xref py py-class docutils literal"><span class="pre">epr.Raster</span></code></a> object.
It read a slice of data from the <a class="reference internal" href="reference.html#epr.Band" title="epr.Band"><code class="xref py py-class docutils literal"><span class="pre">epr.Band</span></code></a> and returns it as a
2D <a class="reference external" href="http://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.html#numpy.ndarray" title="(in NumPy v1.13)"><code class="xref py py-class docutils literal"><span class="pre">numpy.ndarray</span></code></a>.</p>
</li>
</ul>
<span class="target" id="index-15"></span></div>
<div class="section" id="enumerators">
<span id="index-16"></span><h2>Enumerators<a class="headerlink" href="#enumerators" title="Permalink to this headline">¶</a></h2>
<p><a class="reference external" href="https://www.python.org">Python</a> does not have <em>enumerators</em> at language level (at least this is true
for <a class="reference external" href="https://www.python.org">Python</a> < 3.4).
Enumerations are simply mapped as module constants that have the same
name of the C enumerate but are spelled all in capital letters.</p>
<p>For example:</p>
<table border="1" class="docutils">
<colgroup>
<col width="50%" />
<col width="50%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">C</th>
<th class="head">Pythn</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>e_tid_double</td>
<td>E_TID_DOUBLE</td>
</tr>
<tr class="row-odd"><td>e_smod_1OF1</td>
<td>E_SMOD_1OF1</td>
</tr>
<tr class="row-even"><td>e_smid_log</td>
<td>E_SMID_LOG</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="error-handling-and-logging">
<span id="index-17"></span><h2>Error handling and logging<a class="headerlink" href="#error-handling-and-logging" title="Permalink to this headline">¶</a></h2>
<p>Currently error handling and logging functions of the EPR C API are not
exposed to python.</p>
<p>Internal library logging is completely silenced and errors are converted
to <a class="reference external" href="https://www.python.org">Python</a> exceptions.
Where appropriate standard <a class="reference external" href="https://www.python.org">Python</a> exception types are use in other cases
custom exception types (e.g. <a class="reference internal" href="reference.html#epr.EPRError" title="epr.EPRError"><code class="xref py py-exc docutils literal"><span class="pre">epr.EPRError</span></code></a>, <a class="reference internal" href="reference.html#epr.EPRValueError" title="epr.EPRValueError"><code class="xref py py-exc docutils literal"><span class="pre">epr.EPRValueError</span></code></a>)
are used.</p>
</div>
<div class="section" id="library-initialization">
<span id="index-18"></span><h2>Library initialization<a class="headerlink" href="#library-initialization" title="Permalink to this headline">¶</a></h2>
<p>Differently from the C API library initialization is not needed: it is
performed internally the first time the <a class="reference internal" href="reference.html#module-epr" title="epr: Python bindings for ENVISAT Product Reader C API"><code class="xref py py-mod docutils literal"><span class="pre">epr</span></code></a> module is imported
in <a class="reference external" href="https://www.python.org">Python</a>.</p>
</div>
<div class="section" id="high-level-api">
<span id="index-19"></span><h2>High level API<a class="headerlink" href="#high-level-api" title="Permalink to this headline">¶</a></h2>
<p><a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> provides some utility method that has no correspondent in the C API:</p>
<ul class="simple">
<li><a class="reference internal" href="reference.html#epr.Record.fields" title="epr.Record.fields"><code class="xref py py-meth docutils literal"><span class="pre">epr.Record.fields()</span></code></a></li>
<li><a class="reference internal" href="reference.html#epr.Record.get_field_names" title="epr.Record.get_field_names"><code class="xref py py-meth docutils literal"><span class="pre">epr.Record.get_field_names()</span></code></a></li>
<li><a class="reference internal" href="reference.html#epr.Dataset.records" title="epr.Dataset.records"><code class="xref py py-meth docutils literal"><span class="pre">epr.Dataset.records()</span></code></a></li>
<li><a class="reference internal" href="reference.html#epr.Product.get_dataset_names" title="epr.Product.get_dataset_names"><code class="xref py py-meth docutils literal"><span class="pre">epr.Product.get_dataset_names()</span></code></a></li>
<li><a class="reference internal" href="reference.html#epr.Product.get_band_names" title="epr.Product.get_band_names"><code class="xref py py-meth docutils literal"><span class="pre">epr.Product.get_band_names()</span></code></a></li>
<li><a class="reference internal" href="reference.html#epr.Product.datasets" title="epr.Product.datasets"><code class="xref py py-meth docutils literal"><span class="pre">epr.Product.datasets()</span></code></a></li>
<li><a class="reference internal" href="reference.html#epr.Product.bands" title="epr.Product.bands"><code class="xref py py-meth docutils literal"><span class="pre">epr.Product.bands()</span></code></a></li>
</ul>
<p>Example:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">dataset</span> <span class="ow">in</span> <span class="n">product</span><span class="o">.</span><span class="n">datasets</span><span class="p">():</span>
<span class="k">for</span> <span class="n">record</span> <span class="ow">in</span> <span class="n">dataset</span><span class="o">.</span><span class="n">records</span><span class="p">():</span>
<span class="k">print</span><span class="p">(</span><span class="n">record</span><span class="p">)</span>
<span class="k">print</span><span class="p">()</span>
</pre></div>
</div>
<p>Another example:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="s1">'proc_data'</span> <span class="ow">in</span> <span class="n">product</span><span class="o">.</span><span class="n">band_names</span><span class="p">():</span>
<span class="n">band</span> <span class="o">=</span> <span class="n">product</span><span class="o">.</span><span class="n">get_band</span><span class="p">(</span><span class="s1">'proc_data'</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="n">band</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="special-methods">
<span id="index-20"></span><h2>Special methods<a class="headerlink" href="#special-methods" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference external" href="https://www.python.org">Python</a> EPR API also implements some <a class="reference external" href="https://docs.python.org/3/reference/datamodel.html">special method</a> in order to make
EPR programming even handy and, in short, <a class="reference external" href="http://www.cafepy.com/article/be_pythonic">pythonic</a>.</p>
<p>The <code class="docutils literal"><span class="pre">__repr__</span></code> methods have been overridden to provide a little more
information with respect to the standard implementation.</p>
<p>In some cases <code class="docutils literal"><span class="pre">__str__</span></code> method have been overridden to output a verbose
string representation of the objects and their contents.</p>
<p>If the EPR object has a <code class="docutils literal"><span class="pre">print_</span></code> method (like e.g. <a class="reference internal" href="reference.html#epr.Record.print_" title="epr.Record.print_"><code class="xref py py-meth docutils literal"><span class="pre">epr.Record.print_()</span></code></a>
and <a class="reference internal" href="reference.html#epr.Field.print_" title="epr.Field.print_"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.print_()</span></code></a>) then the string representation of the object
will have the same format used by the <code class="docutils literal"><span class="pre">print_</span></code> method.
So writing:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">fd</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="nb">str</span><span class="p">(</span><span class="n">record</span><span class="p">))</span>
</pre></div>
</div>
<p>giver the same result of:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">record</span><span class="o">.</span><span class="n">print_</span><span class="p">(</span><span class="n">fd</span><span class="p">)</span>
</pre></div>
</div>
<p>Of course the <a class="reference internal" href="reference.html#epr.Record.print_" title="epr.Record.print_"><code class="xref py py-meth docutils literal"><span class="pre">epr.Record.print_()</span></code></a> method is more efficient for writing
to file.</p>
<p id="index-21">Also <a class="reference internal" href="reference.html#epr.Dataset" title="epr.Dataset"><code class="xref py py-class docutils literal"><span class="pre">epr.Dataset</span></code></a> and <a class="reference internal" href="reference.html#epr.Record" title="epr.Record"><code class="xref py py-class docutils literal"><span class="pre">epr.Record</span></code></a> classes implement the
<code class="docutils literal"><span class="pre">__iter__</span></code> <a class="reference external" href="https://docs.python.org/3/reference/datamodel.html">special method</a> for iterating over records and fields
respectively.
So it is possible to write code like the following:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">record</span> <span class="ow">in</span> <span class="n">dataset</span><span class="p">:</span>
<span class="k">for</span> <span class="n">index</span><span class="p">,</span> <span class="n">field</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="n">record</span><span class="p">):</span>
<span class="k">print</span><span class="p">(</span><span class="n">index</span><span class="p">,</span> <span class="n">field</span><span class="p">)</span>
</pre></div>
</div>
<p id="index-22"><a class="reference internal" href="reference.html#epr.DSD" title="epr.DSD"><code class="xref py py-class docutils literal"><span class="pre">epr.DSD</span></code></a> and <a class="reference internal" href="reference.html#epr.Field" title="epr.Field"><code class="xref py py-class docutils literal"><span class="pre">epr.Field</span></code></a> classes implement the <code class="docutils literal"><span class="pre">__eq__</span></code>
and <code class="docutils literal"><span class="pre">__ne__</span></code> methods for objects comparison:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">filed1</span> <span class="o">==</span> <span class="n">field2</span><span class="p">:</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'field 1 and field2 are equal'</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="n">field1</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'field1:'</span><span class="p">,</span> <span class="n">field1</span><span class="p">)</span>
<span class="k">print</span><span class="p">(</span><span class="s1">'field2:'</span><span class="p">,</span> <span class="n">field2</span><span class="p">)</span>
</pre></div>
</div>
<p id="index-23"><a class="reference internal" href="reference.html#epr.Field" title="epr.Field"><code class="xref py py-class docutils literal"><span class="pre">epr.Field</span></code></a> object also implement the <code class="docutils literal"><span class="pre">__len__</span></code> special method
that returns the number of elements in the field:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">field</span><span class="o">.</span><span class="n">get_type</span><span class="p">()</span> <span class="o">!=</span> <span class="n">epr</span><span class="o">.</span><span class="n">E_TID_STRING</span><span class="p">:</span>
<span class="k">assert</span> <span class="n">field</span><span class="o">.</span><span class="n">get_num_elems</span><span class="p">()</span> <span class="o">==</span> <span class="nb">len</span><span class="p">(</span><span class="n">field</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">assert</span> <span class="nb">len</span><span class="p">(</span><span class="n">field</span><span class="p">)</span> <span class="o">==</span> <span class="nb">len</span><span class="p">(</span><span class="n">field</span><span class="o">.</span><span class="n">get_elem</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">differently from the <a class="reference internal" href="reference.html#epr.Field.get_num_elems" title="epr.Field.get_num_elems"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.get_num_elems()</span></code></a> method
<code class="docutils literal"><span class="pre">len(field)</span></code> return the number of elements if the field
type is not <a class="reference internal" href="reference.html#epr.E_TID_STRING" title="epr.E_TID_STRING"><code class="xref py py-data docutils literal"><span class="pre">epr.E_TID_STRING</span></code></a>.
If the field contains a string then the string length is
returned.</p>
</div>
<p id="index-24">Finally the <a class="reference internal" href="reference.html#epr.Product" title="epr.Product"><code class="xref py py-class docutils literal"><span class="pre">epr.Product</span></code></a> class acts as a <a class="reference external" href="https://docs.python.org/3/library/stdtypes.html#context-manager-types">context manager</a> (i.e. it
implements the <code class="docutils literal"><span class="pre">__enter__</span></code> and <code class="docutils literal"><span class="pre">__exit__</span></code> methods).</p>
<p>This allows the user to write code like the following:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">epr</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s1">'ASA_IMS_ ... _4650.N1'</span><span class="p">)</span> <span class="k">as</span> <span class="n">product</span><span class="p">:</span>
<span class="k">print</span><span class="p">(</span><span class="n">product</span><span class="p">)</span>
</pre></div>
</div>
<p>that ensure that the product is closed as soon as the program exits the
<code class="docutils literal"><span class="pre">with</span></code> block.</p>
</div>
<div class="section" id="update-support">
<span id="index-25"></span><h2>Update support<a class="headerlink" href="#update-support" title="Permalink to this headline">¶</a></h2>
<p>It is not possible to create new <a class="reference external" href="https://envisat.esa.int">ENVISAT</a> products for scratch with the
EPR API. Indeed EPR means “<strong>E</strong>NVISAT <strong>P</strong>roduct <strong>R</strong>eaeder”.
Anyway, since version 0.9, <a class="reference external" href="https://github.com/avalentino/pyepr">PyEPR</a> also include basic <em>update</em> features.
This means that, while it is still not possible to create new
<code class="xref py py-class docutils literal"><span class="pre">Products</span></code>, the user can <em>update</em> existing ones changing the
contents of any <code class="xref py py-class docutils literal"><span class="pre">Field</span></code> in any record with the only exception of
MPH and SPH <code class="xref py py-class docutils literal"><span class="pre">Field</span></code>s.</p>
<p>The user can open a product in update mode (‘rb+’):</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">product</span> <span class="o">=</span> <span class="n">epr</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s1">'ASA_IMS_ ... _4650.N1'</span><span class="p">,</span> <span class="s1">'rb+'</span><span class="p">)</span>
</pre></div>
</div>
<p>and update the <a class="reference internal" href="reference.html#epr.Field" title="epr.Field"><code class="xref py py-class docutils literal"><span class="pre">epr.Field</span></code></a> element at a specific index:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">field</span><span class="o">.</span><span class="n">set_elem</span><span class="p">(</span><span class="n">new_value</span><span class="p">,</span> <span class="n">index</span><span class="p">)</span>
</pre></div>
</div>
<p>or also update all elements ol the <a class="reference internal" href="reference.html#epr.Field" title="epr.Field"><code class="xref py py-class docutils literal"><span class="pre">epr.Field</span></code></a> in one shot:</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">field</span><span class="o">.</span><span class="n">set_elems</span><span class="p">(</span><span class="n">new_values</span><span class="p">)</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>unfortunately there are some limitations to the update support.
Many of the internal structures of the EPR C API are loaded when the
<code class="xref py py-class docutils literal"><span class="pre">Product</span></code> is opened and are not automatically updated when the
<a class="reference internal" href="reference.html#epr.Field.set_elem" title="epr.Field.set_elem"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.set_elem()</span></code></a> and <a class="reference internal" href="reference.html#epr.Field.set_elems" title="epr.Field.set_elems"><code class="xref py py-meth docutils literal"><span class="pre">epr.Field.set_elems()</span></code></a> methods are
called.
In particular <a class="reference internal" href="reference.html#epr.Band" title="epr.Band"><code class="xref py py-class docutils literal"><span class="pre">epr.Band</span></code></a>s contents may depend on several
<a class="reference internal" href="reference.html#epr.Field" title="epr.Field"><code class="xref py py-class docutils literal"><span class="pre">epr.Field</span></code></a> values, e.g. the contents of <cite>Scaling_Factor_GADS</cite>
<a class="reference internal" href="reference.html#epr.Dataset" title="epr.Dataset"><code class="xref py py-class docutils literal"><span class="pre">epr.Dataset</span></code></a>.
For this reason the user may need to close and re-open the
<a class="reference internal" href="reference.html#epr.Product" title="epr.Product"><code class="xref py py-class docutils literal"><span class="pre">epr.Product</span></code></a> in order to have all changes effectively applied.</p>
<div class="last admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><a class="reference internal" href="update_example.html"><span class="doc">Update Field elements</span></a></p>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">User Manual</a><ul>
<li><a class="reference internal" href="#quick-start">Quick start</a></li>
<li><a class="reference internal" href="#requirements">Requirements</a></li>
<li><a class="reference internal" href="#download">Download</a></li>
<li><a class="reference internal" href="#installation">Installation</a></li>
<li><a class="reference internal" href="#testing">Testing</a></li>
<li><a class="reference internal" href="#python-vs-c-api">Python vs C API</a></li>
<li><a class="reference internal" href="#memory-management">Memory management</a></li>
<li><a class="reference internal" href="#arrays">Arrays</a></li>
<li><a class="reference internal" href="#enumerators">Enumerators</a></li>
<li><a class="reference internal" href="#error-handling-and-logging">Error handling and logging</a></li>
<li><a class="reference internal" href="#library-initialization">Library initialization</a></li>
<li><a class="reference internal" href="#high-level-api">High level API</a></li>
<li><a class="reference internal" href="#special-methods">Special methods</a></li>
<li><a class="reference internal" href="#update-support">Update support</a></li>
</ul>
</li>
</ul>
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