Python async context manager for resource cleanup

<p>I need to create an async context manager for managing resources that need cleanup (database connections, temp files, locks). I want to use it with both <code>async with</code> syntax and as a decorator.</p>

<p>Use <code>@asynccontextmanager</code> or implement <code>__aenter__</code>/<code>__aexit__</code>:</p> <div class="highlight"><pre><span></span><code><span class="kn">from</span><span class="w"> </span><span class="nn">contextlib</span><span class="w"> </span><span class="kn">import</span> <span class="n">asynccontextmanager</span> <span class="kn">from</span><span class="w"> </span><span class="nn">typing</span><span class="w"> </span><span class="kn">import</span> <span class="n">AsyncIterator</span> <span class="c1"># Option 1: Generator-based (simpler for most cases)</span> <span class="nd">@asynccontextmanager</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">managed_transaction</span><span class="p">(</span><span class="n">session</span><span class="p">:</span> <span class="n">AsyncSession</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="n">AsyncIterator</span><span class="p">[</span><span class="n">AsyncSession</span><span class="p">]:</span> <span class="k">async</span> <span class="k">with</span> <span class="n">session</span><span class="o">.</span><span class="n">begin</span><span class="p">():</span> <span class="k">try</span><span class="p">:</span> <span class="k">yield</span> <span class="n">session</span> <span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span> <span class="k">await</span> <span class="n">session</span><span class="o">.</span><span class="n">rollback</span><span class="p">()</span> <span class="k">raise</span> <span class="c1"># Usage:</span> <span class="k">async</span> <span class="k">with</span> <span class="n">managed_transaction</span><span class="p">(</span><span class="n">session</span><span class="p">)</span> <span class="k">as</span> <span class="n">txn</span><span class="p">:</span> <span class="k">await</span> <span class="n">txn</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="n">insert_stmt</span><span class="p">)</span> <span class="c1"># Option 2: Class-based (reusable, configurable)</span> <span class="k">class</span><span class="w"> </span><span class="nc">DistributedLock</span><span class="p">:</span> <span class="k">def</span><span class="w"> </span><span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">redis</span><span class="p">,</span> <span class="n">name</span><span class="p">:</span> <span class="nb">str</span><span class="p">,</span> <span class="n">ttl</span><span class="p">:</span> <span class="nb">int</span> <span class="o">=</span> <span class="mi">30</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">redis</span> <span class="o">=</span> <span class="n">redis</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="sa">f</span><span class="s1">'lock:</span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s1">'</span> <span class="bp">self</span><span class="o">.</span><span class="n">ttl</span> <span class="o">=</span> <span class="n">ttl</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="fm">__aenter__</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="s1">'DistributedLock'</span><span class="p">:</span> <span class="n">acquired</span> <span class="o">=</span> <span class="k">await</span> <span class="bp">self</span><span class="o">.</span><span class="n">redis</span><span class="o">.</span><span class="n">set</span><span class="p">(</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="s1">'1'</span><span class="p">,</span> <span class="n">nx</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="n">ex</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">ttl</span> <span class="p">)</span> <span class="k">if</span> <span class="ow">not</span> <span class="n">acquired</span><span class="p">:</span> <span class="k">raise</span> <span class="n">LockError</span><span class="p">(</span><span class="sa">f</span><span class="s1">'Could not acquire lock: </span><span class="si">{</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span> <span class="k">return</span> <span class="bp">self</span> <span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="fm">__aexit__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc_type</span><span class="p">,</span> <span class="n">exc_val</span><span class="p">,</span> <span class="n">exc_tb</span><span class="p">)</span> <span class="o">-&gt;</span> <span class="kc">None</span><span class="p">:</span> <span class="k">await</span> <span class="bp">self</span><span class="o">.</span><span class="n">redis</span><span class="o">.</span><span class="n">delete</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">)</span> <span class="k">return</span> <span class="kc">False</span> <span class="c1"># Don't suppress exceptions</span> <span class="c1"># Usage:</span> <span class="k">async</span> <span class="k">with</span> <span class="n">DistributedLock</span><span class="p">(</span><span class="n">redis</span><span class="p">,</span> <span class="s1">'embedding-worker'</span><span class="p">):</span> <span class="k">await</span> <span class="n">process_batch</span><span class="p">()</span> </code></pre></div> <p>Key points: - <code>@asynccontextmanager</code> is simpler for one-off contexts - Class-based is better when you need configuration or reuse - Always return <code>False</code> (or <code>None</code>) from <code>__aexit__</code> unless you want to suppress exceptions - <code>async with</code> composes cleanly — use nested contexts for multiple resources</p>