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<div class="section" id="module-pkgutil">
<span id="pkgutil-package-extension-utility"></span><h1>29.3. <a class="reference internal" href="#module-pkgutil" title="pkgutil: Utilities for the import system."><tt class="xref py py-mod docutils literal"><span class="pre">pkgutil</span></tt></a> — Package extension utility<a class="headerlink" href="#module-pkgutil" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/3.2/Lib/pkgutil.py">Lib/pkgutil.py</a></p>
<hr class="docutils" />
<p>This module provides utilities for the import system, in particular package
support.</p>
<dl class="function">
<dt id="pkgutil.extend_path">
<tt class="descclassname">pkgutil.</tt><tt class="descname">extend_path</tt><big>(</big><em>path</em>, <em>name</em><big>)</big><a class="headerlink" href="#pkgutil.extend_path" title="Permalink to this definition">¶</a></dt>
<dd><p>Extend the search path for the modules which comprise a package. Intended
use is to place the following code in a package’s <tt class="file docutils literal"><span class="pre">__init__.py</span></tt>:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">pkgutil</span> <span class="k">import</span> <span class="n">extend_path</span>
<span class="n">__path__</span> <span class="o">=</span> <span class="n">extend_path</span><span class="p">(</span><span class="n">__path__</span><span class="p">,</span> <span class="n">__name__</span><span class="p">)</span>
</pre></div>
</div>
<p>This will add to the package’s <tt class="docutils literal"><span class="pre">__path__</span></tt> all subdirectories of directories
on <tt class="docutils literal"><span class="pre">sys.path</span></tt> named after the package. This is useful if one wants to
distribute different parts of a single logical package as multiple
directories.</p>
<p>It also looks for <tt class="file docutils literal"><span class="pre">*.pkg</span></tt> files beginning where <tt class="docutils literal"><span class="pre">*</span></tt> matches the
<em>name</em> argument. This feature is similar to <tt class="file docutils literal"><span class="pre">*.pth</span></tt> files (see the
<a class="reference internal" href="site.html#module-site" title="site: Module responsible for site-specific configuration."><tt class="xref py py-mod docutils literal"><span class="pre">site</span></tt></a> module for more information), except that it doesn’t special-case
lines starting with <tt class="docutils literal"><span class="pre">import</span></tt>. A <tt class="file docutils literal"><span class="pre">*.pkg</span></tt> file is trusted at face
value: apart from checking for duplicates, all entries found in a
<tt class="file docutils literal"><span class="pre">*.pkg</span></tt> file are added to the path, regardless of whether they exist
on the filesystem. (This is a feature.)</p>
<p>If the input path is not a list (as is the case for frozen packages) it is
returned unchanged. The input path is not modified; an extended copy is
returned. Items are only appended to the copy at the end.</p>
<p>It is assumed that <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> is a sequence. Items of <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>
that are not strings referring to existing directories are ignored. Unicode
items on <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> that cause errors when used as filenames may cause
this function to raise an exception (in line with <a class="reference internal" href="os.path.html#os.path.isdir" title="os.path.isdir"><tt class="xref py py-func docutils literal"><span class="pre">os.path.isdir()</span></tt></a>
behavior).</p>
</dd></dl>
<dl class="class">
<dt id="pkgutil.ImpImporter">
<em class="property">class </em><tt class="descclassname">pkgutil.</tt><tt class="descname">ImpImporter</tt><big>(</big><em>dirname=None</em><big>)</big><a class="headerlink" href="#pkgutil.ImpImporter" title="Permalink to this definition">¶</a></dt>
<dd><p><span class="target" id="index-0"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> Importer that wraps Python’s “classic” import algorithm.</p>
<p>If <em>dirname</em> is a string, a <span class="target" id="index-1"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> importer is created that searches that
directory. If <em>dirname</em> is <tt class="xref docutils literal"><span class="pre">None</span></tt>, a <span class="target" id="index-2"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> importer is created that
searches the current <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>, plus any modules that are frozen or
built-in.</p>
<p>Note that <a class="reference internal" href="#pkgutil.ImpImporter" title="pkgutil.ImpImporter"><tt class="xref py py-class docutils literal"><span class="pre">ImpImporter</span></tt></a> does not currently support being used by
placement on <a class="reference internal" href="sys.html#sys.meta_path" title="sys.meta_path"><tt class="xref py py-data docutils literal"><span class="pre">sys.meta_path</span></tt></a>.</p>
</dd></dl>
<dl class="class">
<dt id="pkgutil.ImpLoader">
<em class="property">class </em><tt class="descclassname">pkgutil.</tt><tt class="descname">ImpLoader</tt><big>(</big><em>fullname</em>, <em>file</em>, <em>filename</em>, <em>etc</em><big>)</big><a class="headerlink" href="#pkgutil.ImpLoader" title="Permalink to this definition">¶</a></dt>
<dd><p><span class="target" id="index-3"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> Loader that wraps Python’s “classic” import algorithm.</p>
</dd></dl>
<dl class="function">
<dt id="pkgutil.find_loader">
<tt class="descclassname">pkgutil.</tt><tt class="descname">find_loader</tt><big>(</big><em>fullname</em><big>)</big><a class="headerlink" href="#pkgutil.find_loader" title="Permalink to this definition">¶</a></dt>
<dd><p>Find a <span class="target" id="index-4"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> “loader” object for <em>fullname</em>.</p>
<p>If <em>fullname</em> contains dots, path must be the containing package’s
<tt class="docutils literal"><span class="pre">__path__</span></tt>. Returns <tt class="xref docutils literal"><span class="pre">None</span></tt> if the module cannot be found or imported.
This function uses <a class="reference internal" href="#pkgutil.iter_importers" title="pkgutil.iter_importers"><tt class="xref py py-func docutils literal"><span class="pre">iter_importers()</span></tt></a>, and is thus subject to the same
limitations regarding platform-specific special import locations such as the
Windows registry.</p>
</dd></dl>
<dl class="function">
<dt id="pkgutil.get_importer">
<tt class="descclassname">pkgutil.</tt><tt class="descname">get_importer</tt><big>(</big><em>path_item</em><big>)</big><a class="headerlink" href="#pkgutil.get_importer" title="Permalink to this definition">¶</a></dt>
<dd><p>Retrieve a <span class="target" id="index-5"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> importer for the given <em>path_item</em>.</p>
<p>The returned importer is cached in <a class="reference internal" href="sys.html#sys.path_importer_cache" title="sys.path_importer_cache"><tt class="xref py py-data docutils literal"><span class="pre">sys.path_importer_cache</span></tt></a> if it was
newly created by a path hook.</p>
<p>If there is no importer, a wrapper around the basic import machinery is
returned. This wrapper is never inserted into the importer cache (<tt class="xref docutils literal"><span class="pre">None</span></tt>
is inserted instead).</p>
<p>The cache (or part of it) can be cleared manually if a rescan of
<a class="reference internal" href="sys.html#sys.path_hooks" title="sys.path_hooks"><tt class="xref py py-data docutils literal"><span class="pre">sys.path_hooks</span></tt></a> is necessary.</p>
</dd></dl>
<dl class="function">
<dt id="pkgutil.get_loader">
<tt class="descclassname">pkgutil.</tt><tt class="descname">get_loader</tt><big>(</big><em>module_or_name</em><big>)</big><a class="headerlink" href="#pkgutil.get_loader" title="Permalink to this definition">¶</a></dt>
<dd><p>Get a <span class="target" id="index-6"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> “loader” object for <em>module_or_name</em>.</p>
<p>If the module or package is accessible via the normal import mechanism, a
wrapper around the relevant part of that machinery is returned. Returns
<tt class="xref docutils literal"><span class="pre">None</span></tt> if the module cannot be found or imported. If the named module is
not already imported, its containing package (if any) is imported, in order
to establish the package <tt class="docutils literal"><span class="pre">__path__</span></tt>.</p>
<p>This function uses <a class="reference internal" href="#pkgutil.iter_importers" title="pkgutil.iter_importers"><tt class="xref py py-func docutils literal"><span class="pre">iter_importers()</span></tt></a>, and is thus subject to the same
limitations regarding platform-specific special import locations such as the
Windows registry.</p>
</dd></dl>
<dl class="function">
<dt id="pkgutil.iter_importers">
<tt class="descclassname">pkgutil.</tt><tt class="descname">iter_importers</tt><big>(</big><em>fullname=''</em><big>)</big><a class="headerlink" href="#pkgutil.iter_importers" title="Permalink to this definition">¶</a></dt>
<dd><p>Yield <span class="target" id="index-7"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> importers for the given module name.</p>
<p>If fullname contains a ‘.’, the importers will be for the package containing
fullname, otherwise they will be importers for <a class="reference internal" href="sys.html#sys.meta_path" title="sys.meta_path"><tt class="xref py py-data docutils literal"><span class="pre">sys.meta_path</span></tt></a>,
<a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>, and Python’s “classic” import machinery, in that order. If
the named module is in a package, that package is imported as a side effect
of invoking this function.</p>
<p>Non-<span class="target" id="index-8"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> mechanisms (e.g. the Windows registry) used by the standard
import machinery to find files in alternative locations are partially
supported, but are searched <em>after</em> <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>. Normally, these
locations are searched <em>before</em> <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>, preventing <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a>
entries from shadowing them.</p>
<p>For this to cause a visible difference in behaviour, there must be a module
or package name that is accessible via both <a class="reference internal" href="sys.html#sys.path" title="sys.path"><tt class="xref py py-data docutils literal"><span class="pre">sys.path</span></tt></a> and one of the
non-<span class="target" id="index-9"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> file system mechanisms. In this case, the emulation will find
the former version, while the builtin import mechanism will find the latter.</p>
<p>Items of the following types can be affected by this discrepancy:
<tt class="docutils literal"><span class="pre">imp.C_EXTENSION</span></tt>, <tt class="docutils literal"><span class="pre">imp.PY_SOURCE</span></tt>, <tt class="docutils literal"><span class="pre">imp.PY_COMPILED</span></tt>,
<tt class="docutils literal"><span class="pre">imp.PKG_DIRECTORY</span></tt>.</p>
</dd></dl>
<dl class="function">
<dt id="pkgutil.iter_modules">
<tt class="descclassname">pkgutil.</tt><tt class="descname">iter_modules</tt><big>(</big><em>path=None</em>, <em>prefix=''</em><big>)</big><a class="headerlink" href="#pkgutil.iter_modules" title="Permalink to this definition">¶</a></dt>
<dd><p>Yields <tt class="docutils literal"><span class="pre">(module_loader,</span> <span class="pre">name,</span> <span class="pre">ispkg)</span></tt> for all submodules on <em>path</em>, or, if
path is <tt class="xref docutils literal"><span class="pre">None</span></tt>, all top-level modules on <tt class="docutils literal"><span class="pre">sys.path</span></tt>.</p>
<p><em>path</em> should be either <tt class="xref docutils literal"><span class="pre">None</span></tt> or a list of paths to look for modules in.</p>
<p><em>prefix</em> is a string to output on the front of every module name on output.</p>
</dd></dl>
<dl class="function">
<dt id="pkgutil.walk_packages">
<tt class="descclassname">pkgutil.</tt><tt class="descname">walk_packages</tt><big>(</big><em>path=None</em>, <em>prefix=''</em>, <em>onerror=None</em><big>)</big><a class="headerlink" href="#pkgutil.walk_packages" title="Permalink to this definition">¶</a></dt>
<dd><p>Yields <tt class="docutils literal"><span class="pre">(module_loader,</span> <span class="pre">name,</span> <span class="pre">ispkg)</span></tt> for all modules recursively on
<em>path</em>, or, if path is <tt class="xref docutils literal"><span class="pre">None</span></tt>, all accessible modules.</p>
<p><em>path</em> should be either <tt class="xref docutils literal"><span class="pre">None</span></tt> or a list of paths to look for modules in.</p>
<p><em>prefix</em> is a string to output on the front of every module name on output.</p>
<p>Note that this function must import all <em>packages</em> (<em>not</em> all modules!) on
the given <em>path</em>, in order to access the <tt class="docutils literal"><span class="pre">__path__</span></tt> attribute to find
submodules.</p>
<p><em>onerror</em> is a function which gets called with one argument (the name of the
package which was being imported) if any exception occurs while trying to
import a package. If no <em>onerror</em> function is supplied, <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><tt class="xref py py-exc docutils literal"><span class="pre">ImportError</span></tt></a>s
are caught and ignored, while all other exceptions are propagated,
terminating the search.</p>
<p>Examples:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="c"># list all modules python can access</span>
<span class="n">walk_packages</span><span class="p">()</span>
<span class="c"># list all submodules of ctypes</span>
<span class="n">walk_packages</span><span class="p">(</span><span class="n">ctypes</span><span class="o">.</span><span class="n">__path__</span><span class="p">,</span> <span class="n">ctypes</span><span class="o">.</span><span class="n">__name__</span> <span class="o">+</span> <span class="s">'.'</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="function">
<dt id="pkgutil.get_data">
<tt class="descclassname">pkgutil.</tt><tt class="descname">get_data</tt><big>(</big><em>package</em>, <em>resource</em><big>)</big><a class="headerlink" href="#pkgutil.get_data" title="Permalink to this definition">¶</a></dt>
<dd><p>Get a resource from a package.</p>
<p>This is a wrapper for the <span class="target" id="index-10"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> loader <a class="reference internal" href="#pkgutil.get_data" title="pkgutil.get_data"><tt class="xref py py-func docutils literal"><span class="pre">get_data()</span></tt></a> API. The
<em>package</em> argument should be the name of a package, in standard module format
(<tt class="docutils literal"><span class="pre">foo.bar</span></tt>). The <em>resource</em> argument should be in the form of a relative
filename, using <tt class="docutils literal"><span class="pre">/</span></tt> as the path separator. The parent directory name
<tt class="docutils literal"><span class="pre">..</span></tt> is not allowed, and nor is a rooted name (starting with a <tt class="docutils literal"><span class="pre">/</span></tt>).</p>
<p>The function returns a binary string that is the contents of the specified
resource.</p>
<p>For packages located in the filesystem, which have already been imported,
this is the rough equivalent of:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">d</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">dirname</span><span class="p">(</span><span class="n">sys</span><span class="o">.</span><span class="n">modules</span><span class="p">[</span><span class="n">package</span><span class="p">]</span><span class="o">.</span><span class="n">__file__</span><span class="p">)</span>
<span class="n">data</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">d</span><span class="p">,</span> <span class="n">resource</span><span class="p">),</span> <span class="s">'rb'</span><span class="p">)</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
</pre></div>
</div>
<p>If the package cannot be located or loaded, or it uses a <span class="target" id="index-11"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0302"><strong>PEP 302</strong></a> loader
which does not support <a class="reference internal" href="#pkgutil.get_data" title="pkgutil.get_data"><tt class="xref py py-func docutils literal"><span class="pre">get_data()</span></tt></a>, then <tt class="xref docutils literal"><span class="pre">None</span></tt> is returned.</p>
</dd></dl>
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