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<div class="section" id="step-2-application-setup-code">
<span id="tutorial-setup"></span><h1>Step 2: Application Setup Code<a class="headerlink" href="#step-2-application-setup-code" title="Permalink to this headline">ΒΆ</a></h1>
<p>Now that we have the schema in place we can create the application module.
Let’s call it <cite>flaskr.py</cite> inside the <cite>flaskr</cite> folder. For starters we
will add the imports we will need as well as the config section. For
small applications it’s a possibility to drop the configuration directly
into the module which we will be doing here. However a cleaner solution
would be to create a separate <cite>.ini</cite> or <cite>.py</cite> file and load that or import
the values from there.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># all the imports</span>
<span class="kn">import</span> <span class="nn">sqlite3</span>
<span class="kn">from</span> <span class="nn">flask</span> <span class="kn">import</span> <span class="n">Flask</span><span class="p">,</span> <span class="n">request</span><span class="p">,</span> <span class="n">session</span><span class="p">,</span> <span class="n">g</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">abort</span><span class="p">,</span> <span class="n">render_template</span><span class="p">,</span> <span class="n">flash</span>
<span class="c"># configuration</span>
<span class="n">DATABASE</span> <span class="o">=</span> <span class="s">'/tmp/flaskr.db'</span>
<span class="n">DEBUG</span> <span class="o">=</span> <span class="bp">True</span>
<span class="n">SECRET_KEY</span> <span class="o">=</span> <span class="s">'development key'</span>
<span class="n">USERNAME</span> <span class="o">=</span> <span class="s">'admin'</span>
<span class="n">PASSWORD</span> <span class="o">=</span> <span class="s">'default'</span>
</pre></div>
</div>
<p>Next we can create our actual application and initialize it with the
config from the same file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># create our little application :)</span>
<span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_object</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
</pre></div>
</div>
<p><a class="reference internal" href="../api.html#flask.Config.from_object" title="flask.Config.from_object"><tt class="xref py py-meth docutils literal"><span class="pre">from_object()</span></tt></a> will look at the given object (if it’s a
string it will import it) and then look for all uppercase variables
defined there. In our case, the configuration we just wrote a few lines
of code above. You can also move that into a separate file.</p>
<p>It is also a good idea to be able to load a configuration from a
configurable file. This is what <a class="reference internal" href="../api.html#flask.Config.from_envvar" title="flask.Config.from_envvar"><tt class="xref py py-meth docutils literal"><span class="pre">from_envvar()</span></tt></a> can
do:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_envvar</span><span class="p">(</span><span class="s">'FLASKR_SETTINGS'</span><span class="p">,</span> <span class="n">silent</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
</div>
<p>That way someone can set an environment variable called
<span class="target" id="index-0"></span><tt class="xref std std-envvar docutils literal"><span class="pre">FLASKR_SETTINGS</span></tt> to specify a config file to be loaded which will
then override the default values. The silent switch just tells Flask to
not complain if no such environment key is set.</p>
<p>The <cite>secret_key</cite> is needed to keep the client-side sessions secure.
Choose that key wisely and as hard to guess and complex as possible. The
debug flag enables or disables the interactive debugger. Never leave
debug mode activated in a production system because it will allow users to
execute code on the server!</p>
<p>We also add a method to easily connect to the database specified. That
can be used to open a connection on request and also from the interactive
Python shell or a script. This will come in handy later.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">connect_db</span><span class="p">():</span>
<span class="k">return</span> <span class="n">sqlite3</span><span class="o">.</span><span class="n">connect</span><span class="p">(</span><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="p">[</span><span class="s">'DATABASE'</span><span class="p">])</span>
</pre></div>
</div>
<p>Finally we just add a line to the bottom of the file that fires up the
server if we want to run that file as a standalone application:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">'__main__'</span><span class="p">:</span>
<span class="n">app</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
</pre></div>
</div>
<p>With that out of the way you should be able to start up the application
without problems. Do this with the following command:</p>
<div class="highlight-python"><pre>python flaskr.py</pre>
</div>
<p>You will see a message telling you that server has started along with
the address at which you can access it.</p>
<p>When you head over to the server in your browser you will get an 404
page not found error because we don’t have any views yet. But we will
focus on that a little later. First we should get the database working.</p>
<div class="admonition-externally-visible-server admonition ">
<p class="first admonition-title">Externally Visible Server</p>
<p class="last">Want your server to be publicly available? Check out the
<a class="reference internal" href="../quickstart.html#public-server"><em>externally visible server</em></a> section for more
information.</p>
</div>
<p>Continue with <a class="reference internal" href="dbinit.html#tutorial-dbinit"><em>Step 3: Creating The Database</em></a>.</p>
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