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306 lines
22 KiB
HTML
<!DOCTYPE html>
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<html lang="en" data-content_root="./">
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<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
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<title>Migrating from Flask — responder 3.6.2 documentation</title>
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<link rel="next" title="Configuration" href="guide-config.html" />
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<link rel="prev" title="Writing Middleware" href="tutorial-middleware.html" />
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<div class="document">
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<div class="documentwrapper">
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<div class="bodywrapper">
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<div class="body" role="main">
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<section id="migrating-from-flask">
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<h1>Migrating from Flask<a class="headerlink" href="#migrating-from-flask" title="Link to this heading">¶</a></h1>
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<p>If you’re coming from Flask, you’ll find Responder familiar but different
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in a few key ways. This guide maps Flask concepts to their Responder
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equivalents and shows you how to translate common patterns.</p>
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<section id="the-big-differences">
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<h2>The Big Differences<a class="headerlink" href="#the-big-differences" title="Link to this heading">¶</a></h2>
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<p><strong>No return values.</strong> In Flask, you return a response. In Responder, you
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mutate it. This is the single biggest difference:</p>
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<p>Flask:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">hello</span><span class="p">():</span>
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<span class="k">return</span> <span class="s2">"hello, world!"</span>
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</pre></div>
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</div>
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<p>Responder:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@api</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="n">req</span><span class="p">,</span> <span class="n">resp</span><span class="p">):</span>
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<span class="n">resp</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"hello, world!"</span>
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</pre></div>
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</div>
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<p><strong>Explicit request and response.</strong> Flask uses a global <code class="docutils literal notranslate"><span class="pre">request</span></code> object
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(via thread-local magic). Responder passes <code class="docutils literal notranslate"><span class="pre">req</span></code> and <code class="docutils literal notranslate"><span class="pre">resp</span></code> explicitly.
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No magic, no import needed — they’re right there in the function signature.</p>
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<p><strong>ASGI, not WSGI.</strong> Flask runs on WSGI, which is synchronous. Responder
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runs on ASGI, which supports async natively. You can still write sync
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views — Responder runs them in a thread pool automatically.</p>
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</section>
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<section id="quick-reference">
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<h2>Quick Reference<a class="headerlink" href="#quick-reference" title="Link to this heading">¶</a></h2>
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<table class="docutils align-default">
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<colgroup>
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<col style="width: 40.0%" />
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<col style="width: 60.0%" />
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</colgroup>
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<thead>
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<tr class="row-odd"><th class="head"><p>Flask</p></th>
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<th class="head"><p>Responder</p></th>
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</tr>
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</thead>
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<tbody>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">Flask(__name__)</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">responder.API()</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">"text"</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">resp.text</span> <span class="pre">=</span> <span class="pre">"text"</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">jsonify(data)</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">resp.media</span> <span class="pre">=</span> <span class="pre">data</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">return</span> <span class="pre">render_template("t.html",</span> <span class="pre">x=1)</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">resp.html</span> <span class="pre">=</span> <span class="pre">api.template("t.html",</span> <span class="pre">x=1)</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">request.args["q"]</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">req.params["q"]</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">request.json</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">await</span> <span class="pre">req.media()</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">request.form</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">await</span> <span class="pre">req.media("form")</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">request.headers["X"]</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">req.headers["X"]</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">request.method</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">req.method</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">request.cookies["x"]</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">req.cookies["x"]</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">session["x"]</span> <span class="pre">=</span> <span class="pre">1</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">resp.session["x"]</span> <span class="pre">=</span> <span class="pre">1</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">abort(404)</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">resp.status_code</span> <span class="pre">=</span> <span class="pre">404</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">redirect("/new")</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">api.redirect(resp,</span> <span class="pre">location="/new")</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">@app.before_request</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">@api.route(before_request=True)</span></code></p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">@app.errorhandler(404)</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">@api.exception_handler(ValueError)</span></code></p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">app.run(debug=True)</span></code></p></td>
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<td><p><code class="docutils literal notranslate"><span class="pre">api.run(debug=True)</span></code></p></td>
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</tr>
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</tbody>
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</table>
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</section>
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<section id="route-parameters">
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<h2>Route Parameters<a class="headerlink" href="#route-parameters" title="Link to this heading">¶</a></h2>
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<p>Flask uses <code class="docutils literal notranslate"><span class="pre"><angle_brackets></span></code>. Responder uses <code class="docutils literal notranslate"><span class="pre">{curly_braces}</span></code>
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with the same type convertor idea:</p>
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<p>Flask:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/users/<int:user_id>"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">get_user</span><span class="p">(</span><span class="n">user_id</span><span class="p">):</span>
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<span class="k">return</span> <span class="n">jsonify</span><span class="p">({</span><span class="s2">"id"</span><span class="p">:</span> <span class="n">user_id</span><span class="p">})</span>
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</pre></div>
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</div>
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<p>Responder:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@api</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/users/{user_id:int}"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">get_user</span><span class="p">(</span><span class="n">req</span><span class="p">,</span> <span class="n">resp</span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">user_id</span><span class="p">):</span>
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<span class="n">resp</span><span class="o">.</span><span class="n">media</span> <span class="o">=</span> <span class="p">{</span><span class="s2">"id"</span><span class="p">:</span> <span class="n">user_id</span><span class="p">}</span>
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</pre></div>
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</div>
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<p>Note the <code class="docutils literal notranslate"><span class="pre">*</span></code> — route parameters are keyword-only arguments in
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Responder. This makes the interface explicit about which arguments
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come from the URL.</p>
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</section>
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<section id="json-apis">
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<h2>JSON APIs<a class="headerlink" href="#json-apis" title="Link to this heading">¶</a></h2>
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<p>Flask:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/api/items"</span><span class="p">,</span> <span class="n">methods</span><span class="o">=</span><span class="p">[</span><span class="s2">"POST"</span><span class="p">])</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">create_item</span><span class="p">():</span>
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<span class="n">data</span> <span class="o">=</span> <span class="n">request</span><span class="o">.</span><span class="n">json</span>
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<span class="c1"># ... create item</span>
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<span class="k">return</span> <span class="n">jsonify</span><span class="p">(</span><span class="n">item</span><span class="p">),</span> <span class="mi">201</span>
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</pre></div>
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</div>
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<p>Responder:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@api</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/api/items"</span><span class="p">,</span> <span class="n">methods</span><span class="o">=</span><span class="p">[</span><span class="s2">"POST"</span><span class="p">])</span>
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<span class="k">async</span> <span class="k">def</span><span class="w"> </span><span class="nf">create_item</span><span class="p">(</span><span class="n">req</span><span class="p">,</span> <span class="n">resp</span><span class="p">):</span>
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<span class="n">data</span> <span class="o">=</span> <span class="k">await</span> <span class="n">req</span><span class="o">.</span><span class="n">media</span><span class="p">()</span>
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<span class="c1"># ... create item</span>
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<span class="n">resp</span><span class="o">.</span><span class="n">media</span> <span class="o">=</span> <span class="n">item</span>
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<span class="n">resp</span><span class="o">.</span><span class="n">status_code</span> <span class="o">=</span> <span class="mi">201</span>
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</pre></div>
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</div>
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<p>The <code class="docutils literal notranslate"><span class="pre">await</span></code> is needed because reading the request body is an async
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I/O operation. This is more explicit than Flask’s approach, and it
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means the event loop isn’t blocked while waiting for the body to arrive.</p>
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</section>
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<section id="templates">
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<h2>Templates<a class="headerlink" href="#templates" title="Link to this heading">¶</a></h2>
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<p>Both use Jinja2. The syntax is nearly identical:</p>
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<p>Flask:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/hello/<name>"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="n">name</span><span class="p">):</span>
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<span class="k">return</span> <span class="n">render_template</span><span class="p">(</span><span class="s2">"hello.html"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>Responder:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nd">@api</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/hello/</span><span class="si">{name}</span><span class="s2">"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">hello</span><span class="p">(</span><span class="n">req</span><span class="p">,</span> <span class="n">resp</span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
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<span class="n">resp</span><span class="o">.</span><span class="n">html</span> <span class="o">=</span> <span class="n">api</span><span class="o">.</span><span class="n">template</span><span class="p">(</span><span class="s2">"hello.html"</span><span class="p">,</span> <span class="n">name</span><span class="o">=</span><span class="n">name</span><span class="p">)</span>
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</pre></div>
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</div>
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</section>
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<section id="blueprints-route-groups">
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<h2>Blueprints → Route Groups<a class="headerlink" href="#blueprints-route-groups" title="Link to this heading">¶</a></h2>
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<p>Flask uses Blueprints to organize routes. Responder has route groups:</p>
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<p>Flask:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">bp</span> <span class="o">=</span> <span class="n">Blueprint</span><span class="p">(</span><span class="s2">"api"</span><span class="p">,</span> <span class="vm">__name__</span><span class="p">,</span> <span class="n">url_prefix</span><span class="o">=</span><span class="s2">"/api"</span><span class="p">)</span>
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<span class="nd">@bp</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/users"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">list_users</span><span class="p">():</span>
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<span class="k">return</span> <span class="n">jsonify</span><span class="p">([])</span>
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<span class="n">app</span><span class="o">.</span><span class="n">register_blueprint</span><span class="p">(</span><span class="n">bp</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>Responder:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">api_v1</span> <span class="o">=</span> <span class="n">api</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s2">"/api"</span><span class="p">)</span>
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<span class="nd">@api_v1</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/users"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">list_users</span><span class="p">(</span><span class="n">req</span><span class="p">,</span> <span class="n">resp</span><span class="p">):</span>
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<span class="n">resp</span><span class="o">.</span><span class="n">media</span> <span class="o">=</span> <span class="p">[]</span>
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</pre></div>
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</div>
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</section>
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<section id="gradual-migration">
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<h2>Gradual Migration<a class="headerlink" href="#gradual-migration" title="Link to this heading">¶</a></h2>
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<p>You don’t have to migrate all at once. Responder can mount your existing
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Flask app at a subroute, so you can move endpoints over one at a time:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">flask</span><span class="w"> </span><span class="kn">import</span> <span class="n">Flask</span>
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<span class="n">flask_app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="vm">__name__</span><span class="p">)</span>
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<span class="c1"># Your existing Flask routes stay here</span>
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<span class="nd">@flask_app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/legacy"</span><span class="p">)</span>
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<span class="k">def</span><span class="w"> </span><span class="nf">legacy</span><span class="p">():</span>
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<span class="k">return</span> <span class="s2">"old endpoint"</span>
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<span class="c1"># Mount Flask under /old, new routes go on Responder</span>
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<span class="n">api</span><span class="o">.</span><span class="n">mount</span><span class="p">(</span><span class="s2">"/old"</span><span class="p">,</span> <span class="n">flask_app</span><span class="p">)</span>
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<span class="nd">@api</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s2">"/new"</span><span class="p">)</span>
|
||
<span class="k">def</span><span class="w"> </span><span class="nf">new_endpoint</span><span class="p">(</span><span class="n">req</span><span class="p">,</span> <span class="n">resp</span><span class="p">):</span>
|
||
<span class="n">resp</span><span class="o">.</span><span class="n">media</span> <span class="o">=</span> <span class="p">{</span><span class="s2">"modern"</span><span class="p">:</span> <span class="kc">True</span><span class="p">}</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>Requests to <code class="docutils literal notranslate"><span class="pre">/old/legacy</span></code> go to Flask. Everything else goes to
|
||
Responder. When you’ve moved everything over, remove the mount.</p>
|
||
</section>
|
||
</section>
|
||
|
||
|
||
</div>
|
||
|
||
</div>
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<div class="sphinxsidebarwrapper"><p class="logo">
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<a href="index.html">
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<img class="logo" src="_static/responder.png" />
|
||
</a>
|
||
</p>
|
||
<p>
|
||
<strong>Responder</strong> — a familiar HTTP service framework for Python.
|
||
<br />
|
||
<small>v3.6.2</small>
|
||
</p>
|
||
<h3>Useful Links</h3>
|
||
<ul>
|
||
<li><a href="https://github.com/kennethreitz/responder">Responder @ GitHub</a></li>
|
||
<li><a href="https://pypi.org/project/responder/">Responder @ PyPI</a></li>
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<li><a href="https://github.com/kennethreitz/responder/issues">Issue Tracker</a></li>
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<h3><a href="index.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#">Migrating from Flask</a><ul>
|
||
<li><a class="reference internal" href="#the-big-differences">The Big Differences</a></li>
|
||
<li><a class="reference internal" href="#quick-reference">Quick Reference</a></li>
|
||
<li><a class="reference internal" href="#route-parameters">Route Parameters</a></li>
|
||
<li><a class="reference internal" href="#json-apis">JSON APIs</a></li>
|
||
<li><a class="reference internal" href="#templates">Templates</a></li>
|
||
<li><a class="reference internal" href="#blueprints-route-groups">Blueprints → Route Groups</a></li>
|
||
<li><a class="reference internal" href="#gradual-migration">Gradual Migration</a></li>
|
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</ul>
|
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</li>
|
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©2018-2026, Kenneth Reitz.
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