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<title>Message Flashing &#8212; Flask Documentation (3.2.x)</title>
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<section id="message-flashing">
<h1>Message Flashing<a class="headerlink" href="#message-flashing" title="Link to this heading"></a></h1>
<p>Good applications and user interfaces are all about feedback. If the user
does not get enough feedback they will probably end up hating the
application. Flask provides a really simple way to give feedback to a
user with the flashing system. The flashing system basically makes it
possible to record a message at the end of a request and access it next
request and only next request. This is usually combined with a layout
template that does this. Note that browsers and sometimes web servers enforce
a limit on cookie sizes. This means that flashing messages that are too
large for session cookies causes message flashing to fail silently.</p>
<section id="simple-flashing">
<h2>Simple Flashing<a class="headerlink" href="#simple-flashing" title="Link to this heading"></a></h2>
<p>So here is a full example:</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="p">,</span> <span class="n">flash</span><span class="p">,</span> <span class="n">redirect</span><span class="p">,</span> <span class="n">render_template</span><span class="p">,</span> \
<span class="n">request</span><span class="p">,</span> <span class="n">url_for</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="n">app</span><span class="o">.</span><span class="n">secret_key</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">&#39;_5#y2L&quot;F4Q8z</span><span class="se">\n\xec</span><span class="s1">]/&#39;</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="n">render_template</span><span class="p">(</span><span class="s1">&#39;index.html&#39;</span><span class="p">)</span>
<span class="nd">@app</span><span class="o">.</span><span class="n">route</span><span class="p">(</span><span class="s1">&#39;/login&#39;</span><span class="p">,</span> <span class="n">methods</span><span class="o">=</span><span class="p">[</span><span class="s1">&#39;GET&#39;</span><span class="p">,</span> <span class="s1">&#39;POST&#39;</span><span class="p">])</span>
<span class="k">def</span><span class="w"> </span><span class="nf">login</span><span class="p">():</span>
<span class="n">error</span> <span class="o">=</span> <span class="kc">None</span>
<span class="k">if</span> <span class="n">request</span><span class="o">.</span><span class="n">method</span> <span class="o">==</span> <span class="s1">&#39;POST&#39;</span><span class="p">:</span>
<span class="k">if</span> <span class="n">request</span><span class="o">.</span><span class="n">form</span><span class="p">[</span><span class="s1">&#39;username&#39;</span><span class="p">]</span> <span class="o">!=</span> <span class="s1">&#39;admin&#39;</span> <span class="ow">or</span> \
<span class="n">request</span><span class="o">.</span><span class="n">form</span><span class="p">[</span><span class="s1">&#39;password&#39;</span><span class="p">]</span> <span class="o">!=</span> <span class="s1">&#39;secret&#39;</span><span class="p">:</span>
<span class="n">error</span> <span class="o">=</span> <span class="s1">&#39;Invalid credentials&#39;</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">flash</span><span class="p">(</span><span class="s1">&#39;You were successfully logged in&#39;</span><span class="p">)</span>
<span class="k">return</span> <span class="n">redirect</span><span class="p">(</span><span class="n">url_for</span><span class="p">(</span><span class="s1">&#39;index&#39;</span><span class="p">))</span>
<span class="k">return</span> <span class="n">render_template</span><span class="p">(</span><span class="s1">&#39;login.html&#39;</span><span class="p">,</span> <span class="n">error</span><span class="o">=</span><span class="n">error</span><span class="p">)</span>
</pre></div>
</div>
<p>And here is the <code class="file docutils literal notranslate"><span class="pre">layout.html</span></code> template which does the magic:</p>
<div class="highlight-html+jinja notranslate"><div class="highlight"><pre><span></span><span class="cp">&lt;!doctype html&gt;</span>
<span class="p">&lt;</span><span class="nt">title</span><span class="p">&gt;</span>My Application<span class="p">&lt;/</span><span class="nt">title</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">with</span> <span class="nv">messages</span> <span class="o">=</span> <span class="nv">get_flashed_messages</span><span class="o">()</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">if</span> <span class="nv">messages</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">ul</span> <span class="na">class</span><span class="o">=</span><span class="s">flashes</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">for</span> <span class="nv">message</span> <span class="k">in</span> <span class="nv">messages</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">li</span><span class="p">&gt;</span><span class="cp">{{</span> <span class="nv">message</span> <span class="cp">}}</span><span class="p">&lt;/</span><span class="nt">li</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
<span class="p">&lt;/</span><span class="nt">ul</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endif</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">endwith</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">block</span> <span class="nv">body</span> <span class="cp">%}{%</span> <span class="k">endblock</span> <span class="cp">%}</span>
</pre></div>
</div>
<p>Here is the <code class="file docutils literal notranslate"><span class="pre">index.html</span></code> template which inherits from <code class="file docutils literal notranslate"><span class="pre">layout.html</span></code>:</p>
<div class="highlight-html+jinja notranslate"><div class="highlight"><pre><span></span><span class="cp">{%</span> <span class="k">extends</span> <span class="s2">&quot;layout.html&quot;</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">block</span> <span class="nv">body</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">h1</span><span class="p">&gt;</span>Overview<span class="p">&lt;/</span><span class="nt">h1</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">p</span><span class="p">&gt;</span>Do you want to <span class="p">&lt;</span><span class="nt">a</span> <span class="na">href</span><span class="o">=</span><span class="s">&quot;</span><span class="cp">{{</span> <span class="nv">url_for</span><span class="o">(</span><span class="s1">&#39;login&#39;</span><span class="o">)</span> <span class="cp">}}</span><span class="s">&quot;</span><span class="p">&gt;</span>log in?<span class="p">&lt;/</span><span class="nt">a</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endblock</span> <span class="cp">%}</span>
</pre></div>
</div>
<p>And here is the <code class="file docutils literal notranslate"><span class="pre">login.html</span></code> template which also inherits from
<code class="file docutils literal notranslate"><span class="pre">layout.html</span></code>:</p>
<div class="highlight-html+jinja notranslate"><div class="highlight"><pre><span></span><span class="cp">{%</span> <span class="k">extends</span> <span class="s2">&quot;layout.html&quot;</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">block</span> <span class="nv">body</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">h1</span><span class="p">&gt;</span>Login<span class="p">&lt;/</span><span class="nt">h1</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">if</span> <span class="nv">error</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">p</span> <span class="na">class</span><span class="o">=</span><span class="s">error</span><span class="p">&gt;&lt;</span><span class="nt">strong</span><span class="p">&gt;</span>Error:<span class="p">&lt;/</span><span class="nt">strong</span><span class="p">&gt;</span> <span class="cp">{{</span> <span class="nv">error</span> <span class="cp">}}</span>
<span class="cp">{%</span> <span class="k">endif</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">form</span> <span class="na">method</span><span class="o">=</span><span class="s">post</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">dl</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">dt</span><span class="p">&gt;</span>Username:
<span class="p">&lt;</span><span class="nt">dd</span><span class="p">&gt;&lt;</span><span class="nt">input</span> <span class="na">type</span><span class="o">=</span><span class="s">text</span> <span class="na">name</span><span class="o">=</span><span class="s">username</span> <span class="na">value</span><span class="o">=</span><span class="s">&quot;</span><span class="cp">{{</span>
<span class="nv">request.form.username</span> <span class="cp">}}</span><span class="s">&quot;</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">dt</span><span class="p">&gt;</span>Password:
<span class="p">&lt;</span><span class="nt">dd</span><span class="p">&gt;&lt;</span><span class="nt">input</span> <span class="na">type</span><span class="o">=</span><span class="s">password</span> <span class="na">name</span><span class="o">=</span><span class="s">password</span><span class="p">&gt;</span>
<span class="p">&lt;/</span><span class="nt">dl</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">p</span><span class="p">&gt;&lt;</span><span class="nt">input</span> <span class="na">type</span><span class="o">=</span><span class="s">submit</span> <span class="na">value</span><span class="o">=</span><span class="s">Login</span><span class="p">&gt;</span>
<span class="p">&lt;/</span><span class="nt">form</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endblock</span> <span class="cp">%}</span>
</pre></div>
</div>
</section>
<section id="flashing-with-categories">
<h2>Flashing With Categories<a class="headerlink" href="#flashing-with-categories" title="Link to this heading"></a></h2>
<details class="changelog">
<summary>Changelog</summary><div class="versionadded">
<p><span class="versionmodified added">Added in version 0.3.</span></p>
</div>
</details><p>It is also possible to provide categories when flashing a message. The
default category if nothing is provided is <code class="docutils literal notranslate"><span class="pre">'message'</span></code>. Alternative
categories can be used to give the user better feedback. For example
error messages could be displayed with a red background.</p>
<p>To flash a message with a different category, just use the second argument
to the <a class="reference internal" href="../api.html#flask.flash" title="flask.flash"><code class="xref py py-func docutils literal notranslate"><span class="pre">flash()</span></code></a> function:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">flash</span><span class="p">(</span><span class="s1">&#39;Invalid password provided&#39;</span><span class="p">,</span> <span class="s1">&#39;error&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p>Inside the template you then have to tell the
<a class="reference internal" href="../api.html#flask.get_flashed_messages" title="flask.get_flashed_messages"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_flashed_messages()</span></code></a> function to also return the
categories. The loop looks slightly different in that situation then:</p>
<div class="highlight-html+jinja notranslate"><div class="highlight"><pre><span></span><span class="cp">{%</span> <span class="k">with</span> <span class="nv">messages</span> <span class="o">=</span> <span class="nv">get_flashed_messages</span><span class="o">(</span><span class="nv">with_categories</span><span class="o">=</span><span class="kp">true</span><span class="o">)</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">if</span> <span class="nv">messages</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">ul</span> <span class="na">class</span><span class="o">=</span><span class="s">flashes</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">for</span> <span class="nv">category</span><span class="o">,</span> <span class="nv">message</span> <span class="k">in</span> <span class="nv">messages</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">li</span> <span class="na">class</span><span class="o">=</span><span class="s">&quot;</span><span class="cp">{{</span> <span class="nv">category</span> <span class="cp">}}</span><span class="s">&quot;</span><span class="p">&gt;</span><span class="cp">{{</span> <span class="nv">message</span> <span class="cp">}}</span><span class="p">&lt;/</span><span class="nt">li</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
<span class="p">&lt;/</span><span class="nt">ul</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endif</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">endwith</span> <span class="cp">%}</span>
</pre></div>
</div>
<p>This is just one example of how to render these flashed messages. One
might also use the category to add a prefix such as
<code class="docutils literal notranslate"><span class="pre">&lt;strong&gt;Error:&lt;/strong&gt;</span></code> to the message.</p>
</section>
<section id="filtering-flash-messages">
<h2>Filtering Flash Messages<a class="headerlink" href="#filtering-flash-messages" title="Link to this heading"></a></h2>
<details class="changelog">
<summary>Changelog</summary><div class="versionadded">
<p><span class="versionmodified added">Added in version 0.9.</span></p>
</div>
</details><p>Optionally you can pass a list of categories which filters the results of
<a class="reference internal" href="../api.html#flask.get_flashed_messages" title="flask.get_flashed_messages"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_flashed_messages()</span></code></a>. This is useful if you wish to
render each category in a separate block.</p>
<div class="highlight-html+jinja notranslate"><div class="highlight"><pre><span></span><span class="cp">{%</span> <span class="k">with</span> <span class="nv">errors</span> <span class="o">=</span> <span class="nv">get_flashed_messages</span><span class="o">(</span><span class="nv">category_filter</span><span class="o">=[</span><span class="s2">&quot;error&quot;</span><span class="o">])</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">if</span> <span class="nv">errors</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">&quot;alert-message block-message error&quot;</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">a</span> <span class="na">class</span><span class="o">=</span><span class="s">&quot;close&quot;</span> <span class="na">href</span><span class="o">=</span><span class="s">&quot;#&quot;</span><span class="p">&gt;</span>×<span class="p">&lt;/</span><span class="nt">a</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">ul</span><span class="p">&gt;</span>
<span class="cp">{%</span>- <span class="k">for</span> <span class="nv">msg</span> <span class="k">in</span> <span class="nv">errors</span> <span class="cp">%}</span>
<span class="p">&lt;</span><span class="nt">li</span><span class="p">&gt;</span><span class="cp">{{</span> <span class="nv">msg</span> <span class="cp">}}</span><span class="p">&lt;/</span><span class="nt">li</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endfor</span> -<span class="cp">%}</span>
<span class="p">&lt;/</span><span class="nt">ul</span><span class="p">&gt;</span>
<span class="p">&lt;/</span><span class="nt">div</span><span class="p">&gt;</span>
<span class="cp">{%</span> <span class="k">endif</span> <span class="cp">%}</span>
<span class="cp">{%</span> <span class="k">endwith</span> <span class="cp">%}</span>
</pre></div>
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<h3>Contents</h3>
<ul>
<li><a class="reference internal" href="#">Message Flashing</a><ul>
<li><a class="reference internal" href="#simple-flashing">Simple Flashing</a></li>
<li><a class="reference internal" href="#flashing-with-categories">Flashing With Categories</a></li>
<li><a class="reference internal" href="#filtering-flash-messages">Filtering Flash Messages</a></li>
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