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<section id="large-applications-as-packages">
<h1>Large Applications as Packages<a class="headerlink" href="#large-applications-as-packages" title="Link to this heading"></a></h1>
<p>Imagine a simple flask application structure that looks like this:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">/</span><span class="n">yourapplication</span>
<span class="n">yourapplication</span><span class="o">.</span><span class="n">py</span>
<span class="o">/</span><span class="n">static</span>
<span class="n">style</span><span class="o">.</span><span class="n">css</span>
<span class="o">/</span><span class="n">templates</span>
<span class="n">layout</span><span class="o">.</span><span class="n">html</span>
<span class="n">index</span><span class="o">.</span><span class="n">html</span>
<span class="n">login</span><span class="o">.</span><span class="n">html</span>
<span class="o">...</span>
</pre></div>
</div>
<p>While this is fine for small applications, for larger applications
it’s a good idea to use a package instead of a module.
The <a class="reference internal" href="../tutorial/index.html"><span class="doc">Tutorial</span></a> is structured to use the package pattern,
see the <a class="reference external" href="https://github.com/pallets/flask/tree/main/examples/tutorial">example code</a>.</p>
<section id="simple-packages">
<h2>Simple Packages<a class="headerlink" href="#simple-packages" title="Link to this heading"></a></h2>
<p>To convert that into a larger one, just create a new folder
<code class="file docutils literal notranslate"><span class="pre">yourapplication</span></code> inside the existing one and move everything below it.
Then rename <code class="file docutils literal notranslate"><span class="pre">yourapplication.py</span></code> to <code class="file docutils literal notranslate"><span class="pre">__init__.py</span></code>. (Make sure to delete
all <code class="docutils literal notranslate"><span class="pre">.pyc</span></code> files first, otherwise things would most likely break)</p>
<p>You should then end up with something like that:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">/</span><span class="n">yourapplication</span>
<span class="o">/</span><span class="n">yourapplication</span>
<span class="fm">__init__</span><span class="o">.</span><span class="n">py</span>
<span class="o">/</span><span class="n">static</span>
<span class="n">style</span><span class="o">.</span><span class="n">css</span>
<span class="o">/</span><span class="n">templates</span>
<span class="n">layout</span><span class="o">.</span><span class="n">html</span>
<span class="n">index</span><span class="o">.</span><span class="n">html</span>
<span class="n">login</span><span class="o">.</span><span class="n">html</span>
<span class="o">...</span>
</pre></div>
</div>
<p>But how do you run your application now? The naive <code class="docutils literal notranslate"><span class="pre">python</span>
<span class="pre">yourapplication/__init__.py</span></code> will not work. Let’s just say that Python
does not want modules in packages to be the startup file. But that is not
a big problem, just add a new file called <code class="file docutils literal notranslate"><span class="pre">pyproject.toml</span></code> next to the inner
<code class="file docutils literal notranslate"><span class="pre">yourapplication</span></code> folder with the following contents:</p>
<div class="highlight-toml notranslate"><div class="highlight"><pre><span></span><span class="k">[project]</span>
<span class="n">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">&quot;yourapplication&quot;</span>
<span class="n">dependencies</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span>
<span class="w"> </span><span class="s2">&quot;flask&quot;</span><span class="p">,</span>
<span class="p">]</span>
<span class="k">[build-system]</span>
<span class="n">requires</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span><span class="s2">&quot;flit_core&lt;4&quot;</span><span class="p">]</span>
<span class="n">build-backend</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s2">&quot;flit_core.buildapi&quot;</span>
</pre></div>
</div>
<p>Install your application so it is importable:</p>
<div class="highlight-text notranslate"><div class="highlight"><pre><span></span>$ pip install -e .
</pre></div>
</div>
<p>To use the <code class="docutils literal notranslate"><span class="pre">flask</span></code> command and run your application you need to set
the <code class="docutils literal notranslate"><span class="pre">--app</span></code> option that tells Flask where to find the application
instance:</p>
<div class="highlight-text notranslate"><div class="highlight"><pre><span></span>$ flask --app yourapplication run
</pre></div>
</div>
<p>What did we gain from this? Now we can restructure the application a bit
into multiple modules. The only thing you have to remember is the
following quick checklist:</p>
<ol class="arabic simple">
<li><p>the <code class="code docutils literal notranslate"><span class="pre">Flask</span></code> application object creation has to be in the
<code class="file docutils literal notranslate"><span class="pre">__init__.py</span></code> file. That way each module can import it safely and the
<code class="code docutils literal notranslate"><span class="pre">__name__</span></code> variable will resolve to the correct package.</p></li>
<li><p>all the view functions (the ones with a <a class="reference internal" href="../api.html#flask.Flask.route" title="flask.Flask.route"><code class="xref py py-meth docutils literal notranslate"><span class="pre">route()</span></code></a>
decorator on top) have to be imported in the <code class="file docutils literal notranslate"><span class="pre">__init__.py</span></code> file.
Not the object itself, but the module it is in. Import the view module
<strong>after the application object is created</strong>.</p></li>
</ol>
<p>Here’s an example <code class="file docutils literal notranslate"><span class="pre">__init__.py</span></code>:</p>
<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>
<span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="vm">__name__</span><span class="p">)</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">yourapplication.views</span>
</pre></div>
</div>
<p>And this is what <code class="file docutils literal notranslate"><span class="pre">views.py</span></code> would look like:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span><span class="w"> </span><span class="nn">yourapplication</span><span class="w"> </span><span class="kn">import</span> <span class="n">app</span>
<span class="nd">@app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s1">&#39;/&#39;</span><span class="p">)</span>
<span class="k">def</span><span class="w"> </span><span class="nf">index</span><span class="p">():</span>
<span class="k">return</span> <span class="s1">&#39;Hello World!&#39;</span>
</pre></div>
</div>
<p>You should then end up with something like that:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">/</span><span class="n">yourapplication</span>
<span class="n">pyproject</span><span class="o">.</span><span class="n">toml</span>
<span class="o">/</span><span class="n">yourapplication</span>
<span class="fm">__init__</span><span class="o">.</span><span class="n">py</span>
<span class="n">views</span><span class="o">.</span><span class="n">py</span>
<span class="o">/</span><span class="n">static</span>
<span class="n">style</span><span class="o">.</span><span class="n">css</span>
<span class="o">/</span><span class="n">templates</span>
<span class="n">layout</span><span class="o">.</span><span class="n">html</span>
<span class="n">index</span><span class="o">.</span><span class="n">html</span>
<span class="n">login</span><span class="o">.</span><span class="n">html</span>
<span class="o">...</span>
</pre></div>
</div>
<div class="admonition-circular-imports admonition">
<p class="admonition-title">Circular Imports</p>
<p>Every Python programmer hates them, and yet we just added some:
circular imports (That’s when two modules depend on each other. In this
case <code class="file docutils literal notranslate"><span class="pre">views.py</span></code> depends on <code class="file docutils literal notranslate"><span class="pre">__init__.py</span></code>). Be advised that this is a
bad idea in general but here it is actually fine. The reason for this is
that we are not actually using the views in <code class="file docutils literal notranslate"><span class="pre">__init__.py</span></code> and just
ensuring the module is imported and we are doing that at the bottom of
the file.</p>
</div>
</section>
<section id="working-with-blueprints">
<h2>Working with Blueprints<a class="headerlink" href="#working-with-blueprints" title="Link to this heading"></a></h2>
<p>If you have larger applications it’s recommended to divide them into
smaller groups where each group is implemented with the help of a
blueprint. For a gentle introduction into this topic refer to the
<a class="reference internal" href="../blueprints.html"><span class="doc">Modular Applications with Blueprints</span></a> chapter of the documentation.</p>
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<h3>Contents</h3>
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<li><a class="reference internal" href="#">Large Applications as Packages</a><ul>
<li><a class="reference internal" href="#simple-packages">Simple Packages</a></li>
<li><a class="reference internal" href="#working-with-blueprints">Working with Blueprints</a></li>
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