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<div class="section" id="message-flashing">
<span id="message-flashing-pattern"></span><h1>Message Flashing<a class="headerlink" href="#message-flashing" title="Permalink to this headline">¶</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.</p>
<div class="section" id="simple-flashing">
<h2>Simple Flashing<a class="headerlink" href="#simple-flashing" title="Permalink to this headline">¶</a></h2>
<p>So here is a full example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">flask</span> <span class="kn">import</span> <span class="n">flash</span><span class="p">,</span> <span class="n">redirect</span><span class="p">,</span> <span class="n">url_for</span><span class="p">,</span> <span class="n">render_template</span>
<span class="nd">@app.route</span><span class="p">(</span><span class="s">'/'</span><span class="p">)</span>
<span class="k">def</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="s">'index.html'</span><span class="p">)</span>
<span class="nd">@app.route</span><span class="p">(</span><span class="s">'/login'</span><span class="p">,</span> <span class="n">methods</span><span class="o">=</span><span class="p">[</span><span class="s">'GET'</span><span class="p">,</span> <span class="s">'POST'</span><span class="p">])</span>
<span class="k">def</span> <span class="nf">login</span><span class="p">():</span>
<span class="n">error</span> <span class="o">=</span> <span class="bp">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="s">'POST'</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="s">'username'</span><span class="p">]</span> <span class="o">!=</span> <span class="s">'admin'</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="s">'password'</span><span class="p">]</span> <span class="o">!=</span> <span class="s">'secret'</span><span class="p">:</span>
<span class="n">error</span> <span class="o">=</span> <span class="s">'Invalid credentials'</span>
<span class="k">else</span><span class="p">:</span>
<span class="n">flash</span><span class="p">(</span><span class="s">'You were successfully logged in'</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="s">'index'</span><span class="p">))</span>
<span class="k">return</span> <span class="n">render_template</span><span class="p">(</span><span class="s">'login.html'</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 the <tt class="docutils literal"><span class="pre">layout.html</span></tt> template which does the magic:</p>
<div class="highlight-html+jinja"><div class="highlight"><pre><span class="cp"><!doctype html></span>
<span class="nt"><title></span>My Application<span class="nt"></title></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="nt"><ul</span> <span class="na">class=</span><span class="s">flashes</span><span class="nt">></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="nt"><li></span><span class="cp">{{</span> <span class="nv">message</span> <span class="cp">}}</span><span class="nt"></li></span>
<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
<span class="nt"></ul></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>And here the index.html template:</p>
<div class="highlight-html+jinja"><div class="highlight"><pre><span class="cp">{%</span> <span class="k">extends</span> <span class="s2">"layout.html"</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="nt"><h1></span>Overview<span class="nt"></h1></span>
<span class="nt"><p></span>Do you want to <span class="nt"><a</span> <span class="na">href=</span><span class="s">"</span><span class="cp">{{</span> <span class="nv">url_for</span><span class="o">(</span><span class="s1">'login'</span><span class="o">)</span> <span class="cp">}}</span><span class="s">"</span><span class="nt">></span>log in?<span class="nt"></a></span>
<span class="cp">{%</span> <span class="k">endblock</span> <span class="cp">%}</span>
</pre></div>
</div>
<p>And of course the login template:</p>
<div class="highlight-html+jinja"><div class="highlight"><pre><span class="cp">{%</span> <span class="k">extends</span> <span class="s2">"layout.html"</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="nt"><h1></span>Login<span class="nt"></h1></span>
<span class="cp">{%</span> <span class="k">if</span> <span class="nv">error</span> <span class="cp">%}</span>
<span class="nt"><p</span> <span class="na">class=</span><span class="s">error</span><span class="nt">><strong></span>Error:<span class="nt"></strong></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="nt"><form</span> <span class="na">action=</span><span class="s">""</span> <span class="na">method=</span><span class="s">post</span><span class="nt">></span>
<span class="nt"><dl></span>
<span class="nt"><dt></span>Username:
<span class="nt"><dd><input</span> <span class="na">type=</span><span class="s">text</span> <span class="na">name=</span><span class="s">username</span> <span class="na">value=</span><span class="s">"</span><span class="cp">{{</span>
<span class="nv">request.form.username</span> <span class="cp">}}</span><span class="s">"</span><span class="nt">></span>
<span class="nt"><dt></span>Password:
<span class="nt"><dd><input</span> <span class="na">type=</span><span class="s">password</span> <span class="na">name=</span><span class="s">password</span><span class="nt">></span>
<span class="nt"></dl></span>
<span class="nt"><p><input</span> <span class="na">type=</span><span class="s">submit</span> <span class="na">value=</span><span class="s">Login</span><span class="nt">></span>
<span class="nt"></form></span>
<span class="cp">{%</span> <span class="k">endblock</span> <span class="cp">%}</span>
</pre></div>
</div>
</div>
<div class="section" id="flashing-with-categories">
<h2>Flashing With Categories<a class="headerlink" href="#flashing-with-categories" title="Permalink to this headline">¶</a></h2>
<p class="versionadded">
<span class="versionmodified">New in version 0.3.</span></p>
<p>It is also possible to provide categories when flashing a message. The
default category if nothing is provided is <tt class="docutils literal"><span class="pre">'message'</span></tt>. 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"><tt class="xref py py-func docutils literal"><span class="pre">flash()</span></tt></a> function:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">flash</span><span class="p">(</span><span class="s">u'Invalid password provided'</span><span class="p">,</span> <span class="s">'error'</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"><tt class="xref py py-func docutils literal"><span class="pre">get_flashed_messages()</span></tt></a> function to also return the
categories. The loop looks slightly different in that situation then:</p>
<div class="highlight-html+jinja"><div class="highlight"><pre><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="nt"><ul</span> <span class="na">class=</span><span class="s">flashes</span><span class="nt">></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="nt"><li</span> <span class="na">class=</span><span class="s">"</span><span class="cp">{{</span> <span class="nv">category</span> <span class="cp">}}</span><span class="s">"</span><span class="nt">></span><span class="cp">{{</span> <span class="nv">message</span> <span class="cp">}}</span><span class="nt"></li></span>
<span class="cp">{%</span> <span class="k">endfor</span> <span class="cp">%}</span>
<span class="nt"></ul></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
<tt class="docutils literal"><span class="pre"><strong>Error:</strong></span></tt> to the message.</p>
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<h3><a href="../index.html">Table Of Contents</a></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>
</ul>
</li>
</ul>
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<li><a href="../index.html">Documentation overview</a><ul>
<li><a href="index.html">Patterns for Flask</a><ul>
<li>Previous: <a href="templateinheritance.html" title="previous chapter">Template Inheritance</a></li>
<li>Next: <a href="jquery.html" title="next chapter">AJAX with jQuery</a></li>
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