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<h1>Source code for networkx.classes.backends</h1><div class="highlight"><pre>
<span></span><span class="sd">"""</span>
<span class="sd">Code to support various backends in a plugin dispatch architecture.</span>
<span class="sd">Create a Dispatcher</span>
<span class="sd">-------------------</span>
<span class="sd">To be a valid plugin, a package must register an entry_point</span>
<span class="sd">of `networkx.plugins` with a key pointing to the handler.</span>
<span class="sd">For example:</span>
<span class="sd">```</span>
<span class="sd">entry_points={'networkx.plugins': 'sparse = networkx_plugin_sparse'}</span>
<span class="sd">```</span>
<span class="sd">The plugin must create a Graph-like object which contains an attribute</span>
<span class="sd">`__networkx_plugin__` with a value of the entry point name.</span>
<span class="sd">Continuing the example above:</span>
<span class="sd">```</span>
<span class="sd">class WrappedSparse:</span>
<span class="sd"> __networkx_plugin__ = "sparse"</span>
<span class="sd"> ...</span>
<span class="sd">```</span>
<span class="sd">When a dispatchable NetworkX algorithm encounters a Graph-like object</span>
<span class="sd">with a `__networkx_plugin__` attribute, it will look for the associated</span>
<span class="sd">dispatch object in the entry_points, load it, and dispatch the work to it.</span>
<span class="sd">Testing</span>
<span class="sd">-------</span>
<span class="sd">To assist in validating the backend algorithm implementations, if an</span>
<span class="sd">environment variable `NETWORKX_GRAPH_CONVERT` is set to a registered</span>
<span class="sd">plugin keys, the dispatch machinery will automatically convert regular</span>
<span class="sd">networkx Graphs and DiGraphs to the backend equivalent by calling</span>
<span class="sd">`<backend dispatcher>.convert_from_nx(G, weight=weight, name=name)`.</span>
<span class="sd">The converted object is then passed to the backend implementation of</span>
<span class="sd">the algorithm. The result is then passed to</span>
<span class="sd">`<backend dispatcher>.convert_to_nx(result, name=name)` to convert back</span>
<span class="sd">to a form expected by the NetworkX tests.</span>
<span class="sd">By defining `convert_from_nx` and `convert_to_nx` methods and setting</span>
<span class="sd">the environment variable, NetworkX will automatically route tests on</span>
<span class="sd">dispatchable algorithms to the backend, allowing the full networkx test</span>
<span class="sd">suite to be run against the backend implementation.</span>
<span class="sd">Example pytest invocation:</span>
<span class="sd">NETWORKX_GRAPH_CONVERT=sparse pytest --pyargs networkx</span>
<span class="sd">Dispatchable algorithms which are not implemented by the backend</span>
<span class="sd">will cause a `pytest.xfail()`, giving some indication that not all</span>
<span class="sd">tests are working, while avoiding causing an explicit failure.</span>
<span class="sd">A special `on_start_tests(items)` function may be defined by the backend.</span>
<span class="sd">It will be called with the list of NetworkX tests discovered. Each item</span>
<span class="sd">is a pytest.Node object. If the backend does not support the test, that</span>
<span class="sd">test can be marked as xfail.</span>
<span class="sd">"""</span>
<span class="kn">import</span> <span class="nn">functools</span>
<span class="kn">import</span> <span class="nn">inspect</span>
<span class="kn">import</span> <span class="nn">os</span>
<span class="kn">import</span> <span class="nn">sys</span>
<span class="kn">from</span> <span class="nn">importlib.metadata</span> <span class="kn">import</span> <span class="n">entry_points</span>
<span class="kn">from</span> <span class="nn">..exception</span> <span class="kn">import</span> <span class="n">NetworkXNotImplemented</span>
<span class="n">__all__</span> <span class="o">=</span> <span class="p">[</span><span class="s2">"_dispatch"</span><span class="p">,</span> <span class="s2">"_mark_tests"</span><span class="p">]</span>
<span class="k">class</span> <span class="nc">PluginInfo</span><span class="p">:</span>
<span class="w"> </span><span class="sd">"""Lazily loaded entry_points plugin information"""</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_items</span> <span class="o">=</span> <span class="kc">None</span>
<span class="k">def</span> <span class="fm">__bool__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">items</span><span class="p">)</span> <span class="o">></span> <span class="mi">0</span>
<span class="nd">@property</span>
<span class="k">def</span> <span class="nf">items</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_items</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">version_info</span> <span class="o"><</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">10</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_items</span> <span class="o">=</span> <span class="n">entry_points</span><span class="p">()[</span><span class="s2">"networkx.plugins"</span><span class="p">]</span>
<span class="k">else</span><span class="p">:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">_items</span> <span class="o">=</span> <span class="n">entry_points</span><span class="p">(</span><span class="n">group</span><span class="o">=</span><span class="s2">"networkx.plugins"</span><span class="p">)</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_items</span>
<span class="k">def</span> <span class="fm">__contains__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">version_info</span> <span class="o"><</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">10</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">len</span><span class="p">([</span><span class="n">ep</span> <span class="k">for</span> <span class="n">ep</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">items</span> <span class="k">if</span> <span class="n">ep</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="n">name</span><span class="p">])</span> <span class="o">></span> <span class="mi">0</span>
<span class="k">return</span> <span class="n">name</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">items</span><span class="o">.</span><span class="n">names</span>
<span class="k">def</span> <span class="fm">__getitem__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">version_info</span> <span class="o"><</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">10</span><span class="p">):</span>
<span class="k">return</span> <span class="p">[</span><span class="n">ep</span> <span class="k">for</span> <span class="n">ep</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">items</span> <span class="k">if</span> <span class="n">ep</span><span class="o">.</span><span class="n">name</span> <span class="o">==</span> <span class="n">name</span><span class="p">][</span><span class="mi">0</span><span class="p">]</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">items</span><span class="p">[</span><span class="n">name</span><span class="p">]</span>
<span class="n">plugins</span> <span class="o">=</span> <span class="n">PluginInfo</span><span class="p">()</span>
<span class="n">_registered_algorithms</span> <span class="o">=</span> <span class="p">{}</span>
<span class="k">def</span> <span class="nf">_register_algo</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">wrapped_func</span><span class="p">):</span>
<span class="k">if</span> <span class="n">name</span> <span class="ow">in</span> <span class="n">_registered_algorithms</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">KeyError</span><span class="p">(</span><span class="sa">f</span><span class="s2">"Algorithm already exists in dispatch registry: </span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="n">_registered_algorithms</span><span class="p">[</span><span class="n">name</span><span class="p">]</span> <span class="o">=</span> <span class="n">wrapped_func</span>
<span class="n">wrapped_func</span><span class="o">.</span><span class="n">dispatchname</span> <span class="o">=</span> <span class="n">name</span>
<div class="viewcode-block" id="_dispatch"><a class="viewcode-back" href="../../../reference/classes/generated/networkx.classes.backends._dispatch.html#networkx.classes.backends._dispatch">[docs]</a><span class="k">def</span> <span class="nf">_dispatch</span><span class="p">(</span><span class="n">func</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="w"> </span><span class="sd">"""Dispatches to a backend algorithm</span>
<span class="sd"> when the first argument is a backend graph-like object.</span>
<span class="sd"> """</span>
<span class="c1"># Allow any of the following decorator forms:</span>
<span class="c1"># - @_dispatch</span>
<span class="c1"># - @_dispatch()</span>
<span class="c1"># - @_dispatch("override_name")</span>
<span class="c1"># - @_dispatch(name="override_name")</span>
<span class="k">if</span> <span class="n">func</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">if</span> <span class="n">name</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">return</span> <span class="n">_dispatch</span>
<span class="k">return</span> <span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="n">_dispatch</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="nb">str</span><span class="p">):</span>
<span class="k">return</span> <span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="n">_dispatch</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">func</span><span class="p">)</span>
<span class="c1"># If name not provided, use the name of the function</span>
<span class="k">if</span> <span class="n">name</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">func</span><span class="o">.</span><span class="vm">__name__</span>
<span class="nd">@functools</span><span class="o">.</span><span class="n">wraps</span><span class="p">(</span><span class="n">func</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">wrapper</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">):</span>
<span class="n">graph</span> <span class="o">=</span> <span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="k">if</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">graph</span><span class="p">,</span> <span class="s2">"__networkx_plugin__"</span><span class="p">)</span> <span class="ow">and</span> <span class="n">plugins</span><span class="p">:</span>
<span class="n">plugin_name</span> <span class="o">=</span> <span class="n">graph</span><span class="o">.</span><span class="n">__networkx_plugin__</span>
<span class="k">if</span> <span class="n">plugin_name</span> <span class="ow">in</span> <span class="n">plugins</span><span class="p">:</span>
<span class="n">backend</span> <span class="o">=</span> <span class="n">plugins</span><span class="p">[</span><span class="n">plugin_name</span><span class="p">]</span><span class="o">.</span><span class="n">load</span><span class="p">()</span>
<span class="k">if</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">backend</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">backend</span><span class="p">,</span> <span class="n">name</span><span class="p">)</span><span class="o">.</span><span class="fm">__call__</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
<span class="k">raise</span> <span class="n">NetworkXNotImplemented</span><span class="p">(</span>
<span class="sa">f</span><span class="s2">"'</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">' not implemented by </span><span class="si">{</span><span class="n">plugin_name</span><span class="si">}</span><span class="s2">"</span>
<span class="p">)</span>
<span class="k">return</span> <span class="n">func</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span>
<span class="n">_register_algo</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">wrapper</span><span class="p">)</span>
<span class="k">return</span> <span class="n">wrapper</span></div>
<span class="k">def</span> <span class="nf">test_override_dispatch</span><span class="p">(</span><span class="n">func</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="w"> </span><span class="sd">"""Auto-converts the first argument into the backend equivalent,</span>
<span class="sd"> causing the dispatching mechanism to trigger for every</span>
<span class="sd"> decorated algorithm."""</span>
<span class="k">if</span> <span class="n">func</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">if</span> <span class="n">name</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="k">return</span> <span class="n">test_override_dispatch</span>
<span class="k">return</span> <span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="n">test_override_dispatch</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">func</span><span class="p">,</span> <span class="nb">str</span><span class="p">):</span>
<span class="k">return</span> <span class="n">functools</span><span class="o">.</span><span class="n">partial</span><span class="p">(</span><span class="n">test_override_dispatch</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">func</span><span class="p">)</span>
<span class="c1"># If name not provided, use the name of the function</span>
<span class="k">if</span> <span class="n">name</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">func</span><span class="o">.</span><span class="vm">__name__</span>
<span class="n">sig</span> <span class="o">=</span> <span class="n">inspect</span><span class="o">.</span><span class="n">signature</span><span class="p">(</span><span class="n">func</span><span class="p">)</span>
<span class="nd">@functools</span><span class="o">.</span><span class="n">wraps</span><span class="p">(</span><span class="n">func</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">wrapper</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">):</span>
<span class="n">backend</span> <span class="o">=</span> <span class="n">plugins</span><span class="p">[</span><span class="n">plugin_name</span><span class="p">]</span><span class="o">.</span><span class="n">load</span><span class="p">()</span>
<span class="k">if</span> <span class="ow">not</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">backend</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="n">pytest</span><span class="o">.</span><span class="n">xfail</span><span class="p">(</span><span class="sa">f</span><span class="s2">"'</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">' not implemented by </span><span class="si">{</span><span class="n">plugin_name</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="n">bound</span> <span class="o">=</span> <span class="n">sig</span><span class="o">.</span><span class="n">bind</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span>
<span class="n">bound</span><span class="o">.</span><span class="n">apply_defaults</span><span class="p">()</span>
<span class="n">graph</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span> <span class="o">=</span> <span class="n">args</span>
<span class="c1"># Convert graph into backend graph-like object</span>
<span class="c1"># Include the weight label, if provided to the algorithm</span>
<span class="n">weight</span> <span class="o">=</span> <span class="kc">None</span>
<span class="k">if</span> <span class="s2">"weight"</span> <span class="ow">in</span> <span class="n">bound</span><span class="o">.</span><span class="n">arguments</span><span class="p">:</span>
<span class="n">weight</span> <span class="o">=</span> <span class="n">bound</span><span class="o">.</span><span class="n">arguments</span><span class="p">[</span><span class="s2">"weight"</span><span class="p">]</span>
<span class="k">elif</span> <span class="s2">"data"</span> <span class="ow">in</span> <span class="n">bound</span><span class="o">.</span><span class="n">arguments</span> <span class="ow">and</span> <span class="s2">"default"</span> <span class="ow">in</span> <span class="n">bound</span><span class="o">.</span><span class="n">arguments</span><span class="p">:</span>
<span class="c1"># This case exists for several MultiGraph edge algorithms</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">bound</span><span class="o">.</span><span class="n">arguments</span><span class="p">[</span><span class="s2">"data"</span><span class="p">],</span> <span class="nb">str</span><span class="p">):</span>
<span class="n">weight</span> <span class="o">=</span> <span class="n">bound</span><span class="o">.</span><span class="n">arguments</span><span class="p">[</span><span class="s2">"data"</span><span class="p">]</span>
<span class="k">elif</span> <span class="n">bound</span><span class="o">.</span><span class="n">arguments</span><span class="p">[</span><span class="s2">"data"</span><span class="p">]:</span>
<span class="n">weight</span> <span class="o">=</span> <span class="s2">"weight"</span>
<span class="n">graph</span> <span class="o">=</span> <span class="n">backend</span><span class="o">.</span><span class="n">convert_from_nx</span><span class="p">(</span><span class="n">graph</span><span class="p">,</span> <span class="n">weight</span><span class="o">=</span><span class="n">weight</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
<span class="n">result</span> <span class="o">=</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">backend</span><span class="p">,</span> <span class="n">name</span><span class="p">)</span><span class="o">.</span><span class="fm">__call__</span><span class="p">(</span><span class="n">graph</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwds</span><span class="p">)</span>
<span class="k">return</span> <span class="n">backend</span><span class="o">.</span><span class="n">convert_to_nx</span><span class="p">(</span><span class="n">result</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
<span class="n">_register_algo</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">wrapper</span><span class="p">)</span>
<span class="k">return</span> <span class="n">wrapper</span>
<span class="c1"># Check for auto-convert testing</span>
<span class="c1"># This allows existing NetworkX tests to be run against a backend</span>
<span class="c1"># implementation without any changes to the testing code. The only</span>
<span class="c1"># required change is to set an environment variable prior to running</span>
<span class="c1"># pytest.</span>
<span class="k">if</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"NETWORKX_GRAPH_CONVERT"</span><span class="p">):</span>
<span class="n">plugin_name</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="p">[</span><span class="s2">"NETWORKX_GRAPH_CONVERT"</span><span class="p">]</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">plugins</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">Exception</span><span class="p">(</span><span class="s2">"No registered networkx.plugins entry_points"</span><span class="p">)</span>
<span class="k">if</span> <span class="n">plugin_name</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">plugins</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">Exception</span><span class="p">(</span>
<span class="sa">f</span><span class="s2">"No registered networkx.plugins entry_point named </span><span class="si">{</span><span class="n">plugin_name</span><span class="si">}</span><span class="s2">"</span>
<span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="kn">import</span> <span class="nn">pytest</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
<span class="k">raise</span> <span class="ne">ImportError</span><span class="p">(</span>
<span class="sa">f</span><span class="s2">"Missing pytest, which is required when using NETWORKX_GRAPH_CONVERT"</span>
<span class="p">)</span>
<span class="c1"># Override `dispatch` for testing</span>
<span class="n">_dispatch</span> <span class="o">=</span> <span class="n">test_override_dispatch</span>
<span class="k">def</span> <span class="nf">_mark_tests</span><span class="p">(</span><span class="n">items</span><span class="p">):</span>
<span class="w"> </span><span class="sd">"""Allow backend to mark tests (skip or xfail) if they aren't able to correctly handle them"""</span>
<span class="k">if</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"NETWORKX_GRAPH_CONVERT"</span><span class="p">):</span>
<span class="n">plugin_name</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="p">[</span><span class="s2">"NETWORKX_GRAPH_CONVERT"</span><span class="p">]</span>
<span class="n">backend</span> <span class="o">=</span> <span class="n">plugins</span><span class="p">[</span><span class="n">plugin_name</span><span class="p">]</span><span class="o">.</span><span class="n">load</span><span class="p">()</span>
<span class="k">if</span> <span class="nb">hasattr</span><span class="p">(</span><span class="n">backend</span><span class="p">,</span> <span class="s2">"on_start_tests"</span><span class="p">):</span>
<span class="nb">getattr</span><span class="p">(</span><span class="n">backend</span><span class="p">,</span> <span class="s2">"on_start_tests"</span><span class="p">)(</span><span class="n">items</span><span class="p">)</span>
</pre></div>
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