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<!DOCTYPE html> <html lang="en" data-content_root="../"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <meta name="viewport" content="width=device-width, initial-scale=1"> <title>The Application Context — Flask Documentation (3.1.x)</title> <link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=4f649999" /> <link rel="stylesheet" type="text/css" href="../_static/flask.css?v=b87c8d14" /> <script src="../_static/documentation_options.js?v=d71c4578"></script> <script src="../_static/doctools.js?v=9bcbadda"></script> <script src="../_static/sphinx_highlight.js?v=dc90522c"></script> <link rel="canonical" href="https://flask.palletsprojects.com/en/stable/appcontext/" /> <link rel="icon" href="../_static/shortcut-icon.png"/> <link rel="index" title="Index" href="../genindex/" /> <link rel="search" title="Search" href="../search/" /> <link rel="next" title="The Request Context" href="../reqcontext/" /> <link rel="prev" title="Application Structure and Lifecycle" href="../lifecycle/" /> <script async type="text/javascript" src="/_/static/javascript/readthedocs-addons.js"></script><meta name="readthedocs-project-slug" content="flask" /><meta name="readthedocs-version-slug" content="stable" /><meta name="readthedocs-resolver-filename" content="/appcontext/" /><meta name="readthedocs-http-status" content="200" /></head><body> <div class="related" role="navigation" aria-label="Related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex/" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex/" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="../reqcontext/" title="The Request Context" accesskey="N">next</a> |</li> <li class="right" > <a href="../lifecycle/" title="Application Structure and Lifecycle" accesskey="P">previous</a> |</li> <li class="nav-item nav-item-0"><a href="../">Flask Documentation (3.1.x)</a> »</li> <li class="nav-item nav-item-this"><a href="">The Application Context</a></li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="the-application-context"> <h1>The Application Context<a class="headerlink" href="#the-application-context" title="Link to this heading">¶</a></h1> <p>The application context keeps track of the application-level data during a request, CLI command, or other activity. Rather than passing the application around to each function, the <a class="reference internal" href="../api/#flask.current_app" title="flask.current_app"><code class="xref py py-data docutils literal notranslate"><span class="pre">current_app</span></code></a> and <a class="reference internal" href="../api/#flask.g" title="flask.g"><code class="xref py py-data docutils literal notranslate"><span class="pre">g</span></code></a> proxies are accessed instead.</p> <p>This is similar to <a class="reference internal" href="../reqcontext/"><span class="doc">The Request Context</span></a>, which keeps track of request-level data during a request. A corresponding application context is pushed when a request context is pushed.</p> <section id="purpose-of-the-context"> <h2>Purpose of the Context<a class="headerlink" href="#purpose-of-the-context" title="Link to this heading">¶</a></h2> <p>The <a class="reference internal" href="../api/#flask.Flask" title="flask.Flask"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flask</span></code></a> application object has attributes, such as <a class="reference internal" href="../api/#flask.Flask.config" title="flask.Flask.config"><code class="xref py py-attr docutils literal notranslate"><span class="pre">config</span></code></a>, that are useful to access within views and <a class="reference internal" href="../cli/"><span class="doc">CLI commands</span></a>. However, importing the <code class="docutils literal notranslate"><span class="pre">app</span></code> instance within the modules in your project is prone to circular import issues. When using the <a class="reference internal" href="../patterns/appfactories/"><span class="doc">app factory pattern</span></a> or writing reusable <a class="reference internal" href="../blueprints/"><span class="doc">blueprints</span></a> or <a class="reference internal" href="../extensions/"><span class="doc">extensions</span></a> there won’t be an <code class="docutils literal notranslate"><span class="pre">app</span></code> instance to import at all.</p> <p>Flask solves this issue with the <em>application context</em>. Rather than referring to an <code class="docutils literal notranslate"><span class="pre">app</span></code> directly, you use the <a class="reference internal" href="../api/#flask.current_app" title="flask.current_app"><code class="xref py py-data docutils literal notranslate"><span class="pre">current_app</span></code></a> proxy, which points to the application handling the current activity.</p> <p>Flask automatically <em>pushes</em> an application context when handling a request. View functions, error handlers, and other functions that run during a request will have access to <a class="reference internal" href="../api/#flask.current_app" title="flask.current_app"><code class="xref py py-data docutils literal notranslate"><span class="pre">current_app</span></code></a>.</p> <p>Flask will also automatically push an app context when running CLI commands registered with <a class="reference internal" href="../api/#flask.Flask.cli" title="flask.Flask.cli"><code class="xref py py-attr docutils literal notranslate"><span class="pre">Flask.cli</span></code></a> using <code class="docutils literal notranslate"><span class="pre">@app.cli.command()</span></code>.</p> </section> <section id="lifetime-of-the-context"> <h2>Lifetime of the Context<a class="headerlink" href="#lifetime-of-the-context" title="Link to this heading">¶</a></h2> <p>The application context is created and destroyed as necessary. When a Flask application begins handling a request, it pushes an application context and a <a class="reference internal" href="../reqcontext/"><span class="doc">request context</span></a>. When the request ends it pops the request context then the application context. Typically, an application context will have the same lifetime as a request.</p> <p>See <a class="reference internal" href="../reqcontext/"><span class="doc">The Request Context</span></a> for more information about how the contexts work and the full life cycle of a request.</p> </section> <section id="manually-push-a-context"> <h2>Manually Push a Context<a class="headerlink" href="#manually-push-a-context" title="Link to this heading">¶</a></h2> <p>If you try to access <a class="reference internal" href="../api/#flask.current_app" title="flask.current_app"><code class="xref py py-data docutils literal notranslate"><span class="pre">current_app</span></code></a>, or anything that uses it, outside an application context, you’ll get this error message:</p> <div class="highlight-pytb notranslate"><div class="highlight"><pre><span></span><span class="x">RuntimeError: Working outside of application context.</span> <span class="x">This typically means that you attempted to use functionality that</span> <span class="x">needed to interface with the current application object in some way.</span> <span class="x">To solve this, set up an application context with app.app_context().</span> </pre></div> </div> <p>If you see that error while configuring your application, such as when initializing an extension, you can push a context manually since you have direct access to the <code class="docutils literal notranslate"><span class="pre">app</span></code>. Use <a class="reference internal" href="../api/#flask.Flask.app_context" title="flask.Flask.app_context"><code class="xref py py-meth docutils literal notranslate"><span class="pre">app_context()</span></code></a> in a <code class="docutils literal notranslate"><span class="pre">with</span></code> block, and everything that runs in the block will have access to <a class="reference internal" href="../api/#flask.current_app" title="flask.current_app"><code class="xref py py-data docutils literal notranslate"><span class="pre">current_app</span></code></a>.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">create_app</span><span class="p">():</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="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">app_context</span><span class="p">():</span> <span class="n">init_db</span><span class="p">()</span> <span class="k">return</span> <span class="n">app</span> </pre></div> </div> <p>If you see that error somewhere else in your code not related to configuring the application, it most likely indicates that you should move that code into a view function or CLI command.</p> </section> <section id="storing-data"> <h2>Storing Data<a class="headerlink" href="#storing-data" title="Link to this heading">¶</a></h2> <p>The application context is a good place to store common data during a request or CLI command. Flask provides the <a class="reference internal" href="../api/#flask.g" title="flask.g"><code class="xref py py-data docutils literal notranslate"><span class="pre">g</span> <span class="pre">object</span></code></a> for this purpose. It is a simple namespace object that has the same lifetime as an application context.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>The <code class="docutils literal notranslate"><span class="pre">g</span></code> name stands for “global”, but that is referring to the data being global <em>within a context</em>. The data on <code class="docutils literal notranslate"><span class="pre">g</span></code> is lost after the context ends, and it is not an appropriate place to store data between requests. Use the <a class="reference internal" href="../api/#flask.session" title="flask.session"><code class="xref py py-data docutils literal notranslate"><span class="pre">session</span></code></a> or a database to store data across requests.</p> </div> <p>A common use for <a class="reference internal" href="../api/#flask.g" title="flask.g"><code class="xref py py-data docutils literal notranslate"><span class="pre">g</span></code></a> is to manage resources during a request.</p> <ol class="arabic simple"> <li><p><code class="docutils literal notranslate"><span class="pre">get_X()</span></code> creates resource <code class="docutils literal notranslate"><span class="pre">X</span></code> if it does not exist, caching it as <code class="docutils literal notranslate"><span class="pre">g.X</span></code>.</p></li> <li><p><code class="docutils literal notranslate"><span class="pre">teardown_X()</span></code> closes or otherwise deallocates the resource if it exists. It is registered as a <a class="reference internal" href="../api/#flask.Flask.teardown_appcontext" title="flask.Flask.teardown_appcontext"><code class="xref py py-meth docutils literal notranslate"><span class="pre">teardown_appcontext()</span></code></a> handler.</p></li> </ol> <p>For example, you can manage a database connection using this pattern:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flask</span> <span class="kn">import</span> <span class="n">g</span> <span class="k">def</span> <span class="nf">get_db</span><span class="p">():</span> <span class="k">if</span> <span class="s1">'db'</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">g</span><span class="p">:</span> <span class="n">g</span><span class="o">.</span><span class="n">db</span> <span class="o">=</span> <span class="n">connect_to_database</span><span class="p">()</span> <span class="k">return</span> <span class="n">g</span><span class="o">.</span><span class="n">db</span> <span class="nd">@app</span><span class="o">.</span><span class="n">teardown_appcontext</span> <span class="k">def</span> <span class="nf">teardown_db</span><span class="p">(</span><span class="n">exception</span><span class="p">):</span> <span class="n">db</span> <span class="o">=</span> <span class="n">g</span><span class="o">.</span><span class="n">pop</span><span class="p">(</span><span class="s1">'db'</span><span class="p">,</span> <span class="kc">None</span><span class="p">)</span> <span class="k">if</span> <span class="n">db</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span><span class="p">:</span> <span class="n">db</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> </pre></div> </div> <p>During a request, every call to <code class="docutils literal notranslate"><span class="pre">get_db()</span></code> will return the same connection, and it will be closed automatically at the end of the request.</p> <p>You can use <a class="reference external" href="https://werkzeug.palletsprojects.com/en/stable/local/#werkzeug.local.LocalProxy" title="(in Werkzeug v3.1.x)"><code class="xref py py-class docutils literal notranslate"><span class="pre">LocalProxy</span></code></a> to make a new context local from <code class="docutils literal notranslate"><span class="pre">get_db()</span></code>:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">werkzeug.local</span> <span class="kn">import</span> <span class="n">LocalProxy</span> <span class="n">db</span> <span class="o">=</span> <span class="n">LocalProxy</span><span class="p">(</span><span class="n">get_db</span><span class="p">)</span> </pre></div> </div> <p>Accessing <code class="docutils literal notranslate"><span class="pre">db</span></code> will call <code class="docutils literal notranslate"><span class="pre">get_db</span></code> internally, in the same way that <a class="reference internal" href="../api/#flask.current_app" title="flask.current_app"><code class="xref py py-data docutils literal notranslate"><span class="pre">current_app</span></code></a> works.</p> </section> <section id="events-and-signals"> <h2>Events and Signals<a class="headerlink" href="#events-and-signals" title="Link to this heading">¶</a></h2> <p>The application will call functions registered with <a class="reference internal" href="../api/#flask.Flask.teardown_appcontext" title="flask.Flask.teardown_appcontext"><code class="xref py py-meth docutils literal notranslate"><span class="pre">teardown_appcontext()</span></code></a> when the application context is popped.</p> <p>The following signals are sent: <a class="reference internal" href="../api/#flask.appcontext_pushed" title="flask.appcontext_pushed"><code class="xref py py-data docutils literal notranslate"><span class="pre">appcontext_pushed</span></code></a>, <a class="reference internal" href="../api/#flask.appcontext_tearing_down" title="flask.appcontext_tearing_down"><code class="xref py py-data docutils literal notranslate"><span class="pre">appcontext_tearing_down</span></code></a>, and <a class="reference internal" href="../api/#flask.appcontext_popped" title="flask.appcontext_popped"><code class="xref py py-data docutils literal notranslate"><span class="pre">appcontext_popped</span></code></a>.</p> </section> </section> <div class="clearer"></div> </div> </div> </div> <span id="sidebar-top"></span> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <p class="logo"><a href="../"> <img class="logo" src="../_static/flask-vertical.png" alt="Logo of Flask"/> </a></p> <h3>Contents</h3> <ul> <li><a class="reference internal" href="#">The Application Context</a><ul> <li><a class="reference internal" href="#purpose-of-the-context">Purpose of the Context</a></li> <li><a class="reference internal" href="#lifetime-of-the-context">Lifetime of the Context</a></li> <li><a class="reference internal" href="#manually-push-a-context">Manually Push a Context</a></li> <li><a class="reference internal" href="#storing-data">Storing Data</a></li> <li><a class="reference internal" href="#events-and-signals">Events and Signals</a></li> </ul> </li> </ul> <h3>Navigation</h3> <ul> <li><a href="../">Overview</a> <ul> <li>Previous: <a href="../lifecycle/" title="previous chapter">Application Structure and Lifecycle</a> <li>Next: <a href="../reqcontext/" title="next chapter">The Request Context</a> </ul> </li> </ul> <search id="searchbox" style="display: none" role="search"> <h3 id="searchlabel">Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search/" method="get"> <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/> <input 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