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| <section id="proxy-futures-f-proxy"> |
| <h1>Proxy futures: <code class="docutils literal notranslate"><span class="pre">f_proxy</span></code><a class="headerlink" href="#proxy-futures-f-proxy" title="Permalink to this headline">¶</a></h1> |
| <p>The <code class="docutils literal notranslate"><span class="pre">f_proxy</span></code> function allows wrapping a future with a proxy which will |
| pass attribute lookups and method calls through to the underlying result, |
| blocking as needed.</p> |
| <p>The primary goal of <code class="docutils literal notranslate"><span class="pre">f_proxy</span></code> is to make it possible to define APIs |
| which support both blocking and non-blocking coding styles.</p> |
| <section id="example"> |
| <h2>Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2> |
| <p>Imagine we have defined some classes as follows:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">DatabaseService</span><span class="p">:</span> |
| <span class="k">def</span> <span class="nf">get_connection</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> |
| <span class="sd">"""Obtain a connection to this application's database.</span> |
| <span class="sd"> Returns a Future[DatabaseConnection]."""</span> |
| <span class="o">...</span> |
| |
| <span class="k">class</span> <span class="nc">DatabaseConnection</span><span class="p">:</span> |
| <span class="k">def</span> <span class="nf">query</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">sql</span><span class="p">,</span> <span class="o">*</span><span class="n">params</span><span class="p">):</span> |
| <span class="sd">"""Perform an SQL query using this connection.</span> |
| <span class="sd"> Returns a Future[DatabaseCursor]."""</span> |
| <span class="o">...</span> |
| |
| <span class="k">class</span> <span class="nc">DatabaseCursor</span><span class="p">:</span> |
| <span class="k">def</span> <span class="fm">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> |
| <span class="sd">"""Iterate over all results referenced by this cursor."""</span> |
| <span class="o">...</span> |
| </pre></div> |
| </div> |
| <p>This API could be used with a non-blocking coding style by composing |
| futures:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">process_results</span><span class="p">(</span><span class="n">cursor</span><span class="p">):</span> |
| <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">cursor</span><span class="p">:</span> |
| <span class="c1"># assume it does something useful with each row</span> |
| <span class="o">...</span> |
| |
| <span class="n">connection</span> <span class="o">=</span> <span class="n">db_service</span><span class="o">.</span><span class="n">get_connection</span><span class="p">()</span> |
| <span class="n">cursor</span> <span class="o">=</span> <span class="n">f_flat_map</span><span class="p">(</span><span class="n">connection</span><span class="p">,</span> <span class="k">lambda</span> <span class="n">c</span><span class="p">:</span> <span class="n">c</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">some_sql</span><span class="p">))</span> |
| <span class="n">results</span> <span class="o">=</span> <span class="n">f_map</span><span class="p">(</span><span class="n">cursor</span><span class="p">,</span> <span class="n">process_results</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>Or it could be used in a blocking coding style by adding calls to |
| <code class="docutils literal notranslate"><span class="pre">.result()</span></code>:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">connection</span> <span class="o">=</span> <span class="n">db_service</span><span class="o">.</span><span class="n">get_connection</span><span class="p">()</span><span class="o">.</span><span class="n">result</span><span class="p">()</span> |
| <span class="n">cursor</span> <span class="o">=</span> <span class="n">connection</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">some_sql</span><span class="p">)</span><span class="o">.</span><span class="n">result</span><span class="p">()</span> |
| <span class="n">results</span> <span class="o">=</span> <span class="n">process_results</span><span class="p">(</span><span class="n">cursor</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <p>If we define the API as returning proxy futures (i.e. wrap each returned |
| future using <code class="docutils literal notranslate"><span class="pre">f_proxy</span></code>), the above two code snippets will continue to |
| work, and the below example also becomes possible: using the API in a |
| blocking coding style without requiring explicit calls to <code class="docutils literal notranslate"><span class="pre">.result()</span></code>:</p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="n">connection</span> <span class="o">=</span> <span class="n">db_service</span><span class="o">.</span><span class="n">get_connection</span><span class="p">()</span> |
| <span class="n">cursor</span> <span class="o">=</span> <span class="n">connection</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">some_sql</span><span class="p">)</span> |
| <span class="n">results</span> <span class="o">=</span> <span class="n">process_results</span><span class="p">(</span><span class="n">cursor</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| <dl class="py function"> |
| <dt class="sig sig-object py" id="more_executors.f_proxy"> |
| <span class="sig-prename descclassname"><span class="pre">more_executors.</span></span><span class="sig-name descname"><span class="pre">f_proxy</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">f</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#more_executors.f_proxy" title="Permalink to this definition">¶</a></dt> |
| <dd><p>Proxy calls on a future through to the future’s result.</p> |
| <p>The value returned by this function is a future resolved with the |
| same result (or exception) as the input future <code class="docutils literal notranslate"><span class="pre">f</span></code>. It will also |
| proxy most attribute lookups and method calls through to the |
| underlying result, awaiting the result when needed.</p> |
| <p>Note that since the returned value is intended to remain usable as |
| a <code class="docutils literal notranslate"><span class="pre">Future</span></code>, this proxy is relatively conservative and avoids |
| proxying functionality which would clash with the <code class="docutils literal notranslate"><span class="pre">Future</span></code> |
| interface.</p> |
| <p>Functionality which is not proxied includes:</p> |
| <ul class="simple"> |
| <li><p>conversion to boolean (<code class="docutils literal notranslate"><span class="pre">__bool__</span></code>)</p></li> |
| <li><p>conversion to string (<code class="docutils literal notranslate"><span class="pre">__str__</span></code>, <code class="docutils literal notranslate"><span class="pre">__repr__</span></code>)</p></li> |
| <li><p>methods relating to object identity (<code class="docutils literal notranslate"><span class="pre">__eq__</span></code>, <code class="docutils literal notranslate"><span class="pre">__hash__</span></code>)</p></li> |
| </ul> |
| <p>Signature: <code class="code docutils literal notranslate"><span class="pre">Future<X></span> <span class="pre">⟶</span> <span class="pre">Future<X></span></code></p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters</dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>f</strong> (<a class="reference external" href="https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.Future" title="(in Python v3.11)"><em>Future</em></a>) – Any future.</p></li> |
| <li><p><strong>timeout</strong> (<a class="reference external" href="https://docs.python.org/3/library/functions.html#float" title="(in Python v3.11)"><em>float</em></a>) – Timeout applied when awaiting the future’s result |
| during proxied calls.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns</dt> |
| <dd class="field-even"><p><dl class="simple"> |
| <dt><a class="reference external" href="https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.Future" title="(in Python v3.11)"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a></dt><dd><p>a Future which proxies calls through to the |
| future’s result as needed.</p> |
| </dd> |
| </dl> |
| </p> |
| </dd> |
| </dl> |
| <div class="versionadded"> |
| <p><span class="versionmodified added">New in version 2.3.0.</span></p> |
| </div> |
| </dd></dl> |
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