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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.annotations">
 <code class="descname">annotations</code><span class="sig-paren">(</span><span class="sig-paren">)</span> &#x2192; Dict[str, Union[bytes, str, google.protobuf.message.Message]]<a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.annotations"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.annotations" title="Permalink to this definition">¶</a></dt>
 <dd></dd></dl>

 <dl class="method">
 <dt id="apache_beam.transforms.ptransform.PTransform.default_type_hints">
 <code class="descname">default_type_hints</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.default_type_hints"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.default_type_hints" 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 v3.9)"><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 v3.9)"><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 v3.9)"><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 v3.9)"><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.with_resource_hints">
 <code class="descname">with_resource_hints</code><span class="sig-paren">(</span><em>**kwargs</em><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.with_resource_hints"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.with_resource_hints" title="Permalink to this definition">¶</a></dt>
 <dd><p>Adds resource hints to the <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>.</p>
 <p>Resource hints allow users to express constraints on the environment where
 the transform should be executed.  Interpretation of the resource hints is
 defined by Beam Runners. Runners may ignore the unsupported hints.</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>**kwargs</strong> – key-value pairs describing hints and their values.</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#ValueError" title="(in Python v3.9)"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> – if provided hints are unknown to the SDK. See
 :mod:~apache_beam.transforms.resources` for a list of known hints.</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.</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.get_resource_hints">
 <code class="descname">get_resource_hints</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="reference internal" href="_modules/apache_beam/transforms/ptransform.html#PTransform.get_resource_hints"><span class="viewcode-link">[source]</span></a><a class="headerlink" href="#apache_beam.transforms.ptransform.PTransform.get_resource_hints" title="Permalink to this definition">¶</a></dt>
 <dd></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>
 <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="nd">@beam</span><span class="o">.</span><span class="n">typehints</span><span class="o">.</span><span class="n">with_input_types</span><span class="p">(</span><span class="o">..</span><span class="p">)</span>
 <span class="nd">@beam</span><span class="o">.</span><span class="n">typehints</span><span class="o">.</span><span class="n">with_output_types</span><span class="p">(</span><span class="o">..</span><span class="p">)</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="nd">@beam</span><span class="o">.</span><span class="n">typehints</span><span class="o">.</span><span class="n">with_input_types</span><span class="p">(</span><span class="o">..</span><span class="p">)</span>
 <span class="nd">@beam</span><span class="o">.</span><span class="n">typehints</span><span class="o">.</span><span class="n">with_output_types</span><span class="p">(</span><span class="o">..</span><span class="p">)</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>
 <p>Type hint support needs to be enabled via the
 –type_check_additional=ptransform_fn flag in Beam 2.
 If CustomMapper is a Cython function, you can still specify input and output
 types provided the decorators appear before &#64;ptransform_fn.</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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