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   <div class="section" id="module-apache_beam.transforms.ptransform">
 <span id="apache-beam-transforms-ptransform-module"></span><h1>apache_beam.transforms.ptransform module<a class="headerlink" href="#module-apache_beam.transforms.ptransform" title="Permalink to this headline">¶</a></h1>
 <p>PTransform and descendants.</p>
 <p>A PTransform is an object describing (not executing) a computation. The actual
 execution semantics for a transform is captured by a runner object. A transform
 object always belongs to a pipeline object.</p>
 <p>A PTransform derived class needs to define the expand() method that describes
 how one or more PValues are created by the transform.</p>
 <p>The module defines a few standard transforms: FlatMap (parallel do),
 GroupByKey (group by key), etc. Note that the expand() methods for these
 classes contain code that will add nodes to the processing graph associated
 with a pipeline.</p>
 <p>As support for the FlatMap transform, the module also defines a DoFn
 class and wrapper class that allows lambda functions to be used as
 FlatMap processing functions.</p>
 <dl class="class">
 <dt id="apache_beam.transforms.ptransform.PTransform">
 <em class="property">class </em><code class="descclassname">apache_beam.transforms.ptransform.</code><code class="descname">PTransform</code><span class="sig-paren">(</span><em>label=None</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform" title="Permalink to this definition">¶</a></dt>
 <dd><p>Bases: <a class="reference internal" href="apache_beam.typehints.decorators.html#apache_beam.typehints.decorators.WithTypeHints" title="apache_beam.typehints.decorators.WithTypeHints"><code class="xref py py-class docutils literal notranslate"><span class="pre">apache_beam.typehints.decorators.WithTypeHints</span></code></a>, <a class="reference internal" href="apache_beam.transforms.display.html#apache_beam.transforms.display.HasDisplayData" title="apache_beam.transforms.display.HasDisplayData"><code class="xref py py-class docutils literal notranslate"><span class="pre">apache_beam.transforms.display.HasDisplayData</span></code></a></p>
 <p>A transform object used to modify one or more PCollections.</p>
 <p>Subclasses must define an expand() method that will be used when the transform
 is applied to some arguments. Typical usage pattern will be:</p>
 <blockquote>
 <div>input | CustomTransform(…)</div></blockquote>
 <p>The expand() method of the CustomTransform object passed in will be called
 with input as an argument.</p>
 <dl class="attribute">
 <dt id="apache_beam.transforms.ptransform.PTransform.side_inputs">
 <code class="descname">side_inputs</code><em class="property"> = ()</em><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.side_inputs" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="attribute">
 <dt id="apache_beam.transforms.ptransform.PTransform.pipeline">
 <code class="descname">pipeline</code><em class="property"> = None</em><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.pipeline" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="attribute">
 <dt id="apache_beam.transforms.ptransform.PTransform.label">
 <code class="descname">label</code><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.label" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.default_label">
 <code class="descname">default_label</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.default_label"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.default_label" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.with_input_types">
 <code class="descname">with_input_types</code><span class="sig-paren">(</span><em>input_type_hint</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.with_input_types"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.with_input_types" title="Permalink to this definition">¶</a></dt>
 <dd><p>Annotates the input type of a <a class="reference internal" href="#apache_beam.transforms.ptransform.PTransform" title="apache_beam.transforms.ptransform.PTransform"><code class="xref py py-class docutils literal notranslate"><span class="pre">PTransform</span></code></a> with a type-hint.</p>
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>input_type_hint</strong> (<a class="reference external" href="https://docs.python.org/3/library/functions.html#type" title="(in Python v3.8)"><em>type</em></a>) – An instance of an allowed built-in type, a custom
 class, or an instance of a
 <code class="xref py py-class docutils literal notranslate"><span class="pre">TypeConstraint</span></code>.</td>
 </tr>
 <tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><a class="reference external" href="https://docs.python.org/3/library/exceptions.html#TypeError" title="(in Python v3.8)"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> – If <strong>input_type_hint</strong> is not a valid type-hint.
 See
 <code class="xref py py-obj docutils literal notranslate"><span class="pre">apache_beam.typehints.typehints.validate_composite_type_param()</span></code>
 for further details.</td>
 </tr>
 <tr class="field-odd field"><th class="field-name">Returns:</th><td class="field-body">A reference to the instance of this particular
 <a class="reference internal" href="#apache_beam.transforms.ptransform.PTransform" title="apache_beam.transforms.ptransform.PTransform"><code class="xref py py-class docutils literal notranslate"><span class="pre">PTransform</span></code></a> object. This allows chaining type-hinting related
 methods.</td>
 </tr>
 <tr class="field-even field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference internal" href="#apache_beam.transforms.ptransform.PTransform" title="apache_beam.transforms.ptransform.PTransform">PTransform</a></td>
 </tr>
 </tbody>
 </table>
 </dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.with_output_types">
 <code class="descname">with_output_types</code><span class="sig-paren">(</span><em>type_hint</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.with_output_types"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.with_output_types" title="Permalink to this definition">¶</a></dt>
 <dd><p>Annotates the output type of a <a class="reference internal" href="#apache_beam.transforms.ptransform.PTransform" title="apache_beam.transforms.ptransform.PTransform"><code class="xref py py-class docutils literal notranslate"><span class="pre">PTransform</span></code></a> with a type-hint.</p>
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>type_hint</strong> (<a class="reference external" href="https://docs.python.org/3/library/functions.html#type" title="(in Python v3.8)"><em>type</em></a>) – An instance of an allowed built-in type, a custom class,
 or a <code class="xref py py-class docutils literal notranslate"><span class="pre">TypeConstraint</span></code>.</td>
 </tr>
 <tr class="field-even field"><th class="field-name">Raises:</th><td class="field-body"><a class="reference external" href="https://docs.python.org/3/library/exceptions.html#TypeError" title="(in Python v3.8)"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a> – If <strong>type_hint</strong> is not a valid type-hint. See
 <code class="xref py py-obj docutils literal notranslate"><span class="pre">validate_composite_type_param()</span></code>
 for further details.</td>
 </tr>
 <tr class="field-odd field"><th class="field-name">Returns:</th><td class="field-body">A reference to the instance of this particular
 <a class="reference internal" href="#apache_beam.transforms.ptransform.PTransform" title="apache_beam.transforms.ptransform.PTransform"><code class="xref py py-class docutils literal notranslate"><span class="pre">PTransform</span></code></a> object. This allows chaining type-hinting related
 methods.</td>
 </tr>
 <tr class="field-even field"><th class="field-name">Return type:</th><td class="field-body"><a class="reference internal" href="#apache_beam.transforms.ptransform.PTransform" title="apache_beam.transforms.ptransform.PTransform">PTransform</a></td>
 </tr>
 </tbody>
 </table>
 </dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.type_check_inputs">
 <code class="descname">type_check_inputs</code><span class="sig-paren">(</span><em>pvalueish</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.type_check_inputs"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.type_check_inputs" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.infer_output_type">
 <code class="descname">infer_output_type</code><span class="sig-paren">(</span><em>unused_input_type</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.infer_output_type"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.infer_output_type" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.type_check_outputs">
 <code class="descname">type_check_outputs</code><span class="sig-paren">(</span><em>pvalueish</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.type_check_outputs"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.type_check_outputs" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.type_check_inputs_or_outputs">
 <code class="descname">type_check_inputs_or_outputs</code><span class="sig-paren">(</span><em>pvalueish</em>, <em>input_or_output</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.type_check_inputs_or_outputs"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.type_check_inputs_or_outputs" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.expand">
 <code class="descname">expand</code><span class="sig-paren">(</span><em>input_or_inputs</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.expand"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.expand" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.get_windowing">
 <code class="descname">get_windowing</code><span class="sig-paren">(</span><em>inputs</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.get_windowing"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.get_windowing" title="Permalink to this definition">¶</a></dt>
 <dd><p>Returns the window function to be associated with transform’s output.</p>
 <p>By default most transforms just return the windowing function associated
 with the input PCollection (or the first input if several).</p>
 </dd></dl>

 <dl class="classmethod">
 <dt id="apache_beam.transforms.ptransform.PTransform.register_urn">
 <em class="property">classmethod </em><code class="descname">register_urn</code><span class="sig-paren">(</span><em>urn</em>, <em>parameter_type</em>, <em>constructor=None</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.register_urn"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.register_urn" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.to_runner_api">
 <code class="descname">to_runner_api</code><span class="sig-paren">(</span><em>context</em>, <em>has_parts=False</em>, <em>**extra_kwargs</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.to_runner_api"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.to_runner_api" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="classmethod">
 <dt id="apache_beam.transforms.ptransform.PTransform.from_runner_api">
 <em class="property">classmethod </em><code class="descname">from_runner_api</code><span class="sig-paren">(</span><em>proto</em>, <em>context</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.from_runner_api"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.from_runner_api" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.to_runner_api_parameter">
 <code class="descname">to_runner_api_parameter</code><span class="sig-paren">(</span><em>unused_context</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.to_runner_api_parameter"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.to_runner_api_parameter" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.to_runner_api_pickled">
 <code class="descname">to_runner_api_pickled</code><span class="sig-paren">(</span><em>unused_context</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.to_runner_api_pickled"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.to_runner_api_pickled" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.runner_api_requires_keyed_input">
 <code class="descname">runner_api_requires_keyed_input</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.runner_api_requires_keyed_input"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.runner_api_requires_keyed_input" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 </dd></dl>

 <dl class="function">
 <dt id="apache_beam.transforms.ptransform.ptransform_fn">
 <code class="descclassname">apache_beam.transforms.ptransform.</code><code class="descname">ptransform_fn</code><span class="sig-paren">(</span><em>fn</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#ptransform_fn"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.ptransform_fn" title="Permalink to this definition">¶</a></dt>
 <dd><p>A decorator for a function-based PTransform.</p>
 <p>Experimental; no backwards-compatibility guarantees.</p>
 <table class="docutils field-list" frame="void" rules="none">
 <col class="field-name" />
 <col class="field-body" />
 <tbody valign="top">
 <tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><strong>fn</strong> – A function implementing a custom PTransform.</td>
 </tr>
 <tr class="field-even field"><th class="field-name">Returns:</th><td class="field-body">A CallablePTransform instance wrapping the function-based PTransform.</td>
 </tr>
 </tbody>
 </table>
 <p>This wrapper provides an alternative, simpler way to define a PTransform.
 The standard method is to subclass from PTransform and override the expand()
 method. An equivalent effect can be obtained by defining a function that
 accepts an input PCollection and additional optional arguments and returns a
 resulting PCollection. For example:</p>
 <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@ptransform_fn</span>
 <span class="k">def</span> <span class="nf">CustomMapper</span><span class="p">(</span><span class="n">pcoll</span><span class="p">,</span> <span class="n">mapfn</span><span class="p">):</span>
   <span class="k">return</span> <span class="n">pcoll</span> <span class="o">|</span> <span class="n">ParDo</span><span class="p">(</span><span class="n">mapfn</span><span class="p">)</span>
 </pre></div>
 </div>
 <p>The equivalent approach using PTransform subclassing:</p>
 <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">CustomMapper</span><span class="p">(</span><span class="n">PTransform</span><span class="p">):</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="n">mapfn</span><span class="p">):</span>
     <span class="nb">super</span><span class="p">(</span><span class="n">CustomMapper</span><span class="p">,</span> <span class="bp">self</span><span class="p">)</span><span class="o">.</span><span class="fm">__init__</span><span class="p">()</span>
     <span class="bp">self</span><span class="o">.</span><span class="n">mapfn</span> <span class="o">=</span> <span class="n">mapfn</span>

   <span class="k">def</span> <span class="nf">expand</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">pcoll</span><span class="p">):</span>
     <span class="k">return</span> <span class="n">pcoll</span> <span class="o">|</span> <span class="n">ParDo</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">mapfn</span><span class="p">)</span>
 </pre></div>
 </div>
 <p>With either method the custom PTransform can be used in pipelines as if
 it were one of the “native” PTransforms:</p>
 <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">result_pcoll</span> <span class="o">=</span> <span class="n">input_pcoll</span> <span class="o">|</span> <span class="s1">&#39;Label&#39;</span> <span class="o">&gt;&gt;</span> <span class="n">CustomMapper</span><span class="p">(</span><span class="n">somefn</span><span class="p">)</span>
 </pre></div>
 </div>
 <p>Note that for both solutions the underlying implementation of the pipe
 operator (i.e., <cite>|</cite>) will inject the pcoll argument in its proper place
 (first argument if no label was specified and second argument otherwise).</p>
 </dd></dl>

 <dl class="function">
 <dt id="apache_beam.transforms.ptransform.label_from_callable">
 <code class="descclassname">apache_beam.transforms.ptransform.</code><code class="descname">label_from_callable</code><span class="sig-paren">(</span><em>fn</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#label_from_callable"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.label_from_callable" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 </div>


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