diff options
Diffstat (limited to 'studio/static/doc/flask-docs/patterns/lazyloading.html')
| -rw-r--r-- | studio/static/doc/flask-docs/patterns/lazyloading.html | 214 |
1 files changed, 214 insertions, 0 deletions
diff --git a/studio/static/doc/flask-docs/patterns/lazyloading.html b/studio/static/doc/flask-docs/patterns/lazyloading.html new file mode 100644 index 0000000..982b86a --- /dev/null +++ b/studio/static/doc/flask-docs/patterns/lazyloading.html @@ -0,0 +1,214 @@ + +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> + + +<html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> + + <title>Lazily Loading Views — Flask 0.8 documentation</title> + + <link rel="stylesheet" href="../_static/flasky.css" type="text/css" /> + <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> + + <script type="text/javascript"> + var DOCUMENTATION_OPTIONS = { + URL_ROOT: '../', + VERSION: '0.8', + COLLAPSE_INDEX: false, + FILE_SUFFIX: '.html', + HAS_SOURCE: true + }; + </script> + <script type="text/javascript" src="../_static/jquery.js"></script> + <script type="text/javascript" src="../_static/underscore.js"></script> + <script type="text/javascript" src="../_static/doctools.js"></script> + <link rel="top" title="Flask 0.8 documentation" href="../index.html" /> + <link rel="up" title="Patterns for Flask" href="index.html" /> + <link rel="next" title="MongoKit in Flask" href="mongokit.html" /> + <link rel="prev" title="Custom Error Pages" href="errorpages.html" /> + + + <link rel="apple-touch-icon" href="../_static/touch-icon.png" /> + + <link media="only screen and (max-device-width: 480px)" href="../_static/small_flask.css" type= "text/css" rel="stylesheet" /> + + </head> + <body> + <div class="related"> + <h3>Navigation</h3> + <ul> + <li class="right" style="margin-right: 10px"> + <a href="../genindex.html" title="General Index" + accesskey="I">index</a></li> + <li class="right" > + <a href="mongokit.html" title="MongoKit in Flask" + accesskey="N">next</a> |</li> + <li class="right" > + <a href="errorpages.html" title="Custom Error Pages" + accesskey="P">previous</a> |</li> + <li><a href="../index.html">Flask 0.8 documentation</a> »</li> + <li><a href="index.html" accesskey="U">Patterns for Flask</a> »</li> + </ul> + </div> + + <div class="document"> + <div class="documentwrapper"> + <div class="bodywrapper"> + <div class="body"> + + <div class="section" id="lazily-loading-views"> +<h1>Lazily Loading Views<a class="headerlink" href="#lazily-loading-views" title="Permalink to this headline">¶</a></h1> +<p>Flask is usually used with the decorators. Decorators are simple and you +have the URL right next to the function that is called for that specific +URL. However there is a downside to this approach: it means all your code +that uses decorators has to be imported upfront or Flask will never +actually find your function.</p> +<p>This can be a problem if your application has to import quick. It might +have to do that on systems like Google’s App Engine or other systems. So +if you suddenly notice that your application outgrows this approach you +can fall back to a centralized URL mapping.</p> +<p>The system that enables having a central URL map is the +<a class="reference internal" href="../api.html#flask.Flask.add_url_rule" title="flask.Flask.add_url_rule"><tt class="xref py py-meth docutils literal"><span class="pre">add_url_rule()</span></tt></a> function. Instead of using decorators, +you have a file that sets up the application with all URLs.</p> +<div class="section" id="converting-to-centralized-url-map"> +<h2>Converting to Centralized URL Map<a class="headerlink" href="#converting-to-centralized-url-map" title="Permalink to this headline">¶</a></h2> +<p>Imagine the current application looks somewhat like this:</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">Flask</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="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">pass</span> + +<span class="nd">@app.route</span><span class="p">(</span><span class="s">'/user/<username>'</span><span class="p">)</span> +<span class="k">def</span> <span class="nf">user</span><span class="p">(</span><span class="n">username</span><span class="p">):</span> + <span class="k">pass</span> +</pre></div> +</div> +<p>Then the centralized approach you would have one file with the views +(<cite>views.py</cite>) but without any decorator:</p> +<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">index</span><span class="p">():</span> + <span class="k">pass</span> + +<span class="k">def</span> <span class="nf">user</span><span class="p">(</span><span class="n">username</span><span class="p">):</span> + <span class="k">pass</span> +</pre></div> +</div> +<p>And then a file that sets up an application which maps the functions to +URLs:</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">Flask</span> +<span class="kn">from</span> <span class="nn">yourapplication</span> <span class="kn">import</span> <span class="n">views</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">add_url_rule</span><span class="p">(</span><span class="s">'/'</span><span class="p">,</span> <span class="n">view_func</span><span class="o">=</span><span class="n">views</span><span class="o">.</span><span class="n">index</span><span class="p">)</span> +<span class="n">app</span><span class="o">.</span><span class="n">add_url_rule</span><span class="p">(</span><span class="s">'/user/<username>'</span><span class="p">,</span> <span class="n">view_func</span><span class="o">=</span><span class="n">views</span><span class="o">.</span><span class="n">user</span><span class="p">)</span> +</pre></div> +</div> +</div> +<div class="section" id="loading-late"> +<h2>Loading Late<a class="headerlink" href="#loading-late" title="Permalink to this headline">¶</a></h2> +<p>So far we only split up the views and the routing, but the module is still +loaded upfront. The trick to actually load the view function as needed. +This can be accomplished with a helper class that behaves just like a +function but internally imports the real function on first use:</p> +<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">werkzeug</span> <span class="kn">import</span> <span class="n">import_string</span><span class="p">,</span> <span class="n">cached_property</span> + +<span class="k">class</span> <span class="nc">LazyView</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span> + + <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">import_name</span><span class="p">):</span> + <span class="bp">self</span><span class="o">.</span><span class="n">__module__</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">__name__</span> <span class="o">=</span> <span class="n">import_name</span><span class="o">.</span><span class="n">rsplit</span><span class="p">(</span><span class="s">'.'</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span> + <span class="bp">self</span><span class="o">.</span><span class="n">import_name</span> <span class="o">=</span> <span class="n">import_name</span> + + <span class="nd">@cached_property</span> + <span class="k">def</span> <span class="nf">view</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> + <span class="k">return</span> <span class="n">import_string</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">import_name</span><span class="p">)</span> + + <span class="k">def</span> <span class="nf">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span> + <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">view</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">)</span> +</pre></div> +</div> +<p>What’s important here is is that <cite>__module__</cite> and <cite>__name__</cite> are properly +set. This is used by Flask internally to figure out how to name the +URL rules in case you don’t provide a name for the rule yourself.</p> +<p>Then you can define your central place to combine the views like this:</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">Flask</span> +<span class="kn">from</span> <span class="nn">yourapplication.helpers</span> <span class="kn">import</span> <span class="n">LazyView</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">add_url_rule</span><span class="p">(</span><span class="s">'/'</span><span class="p">,</span> + <span class="n">view_func</span><span class="o">=</span><span class="n">LazyView</span><span class="p">(</span><span class="s">'yourapplication.views.index'</span><span class="p">))</span> +<span class="n">app</span><span class="o">.</span><span class="n">add_url_rule</span><span class="p">(</span><span class="s">'/user/<username>'</span><span class="p">,</span> + <span class="n">view_func</span><span class="o">=</span><span class="n">LazyView</span><span class="p">(</span><span class="s">'yourapplication.views.user'</span><span class="p">))</span> +</pre></div> +</div> +<p>You can further optimize this in terms of amount of keystrokes needed to +write this by having a function that calls into +<a class="reference internal" href="../api.html#flask.Flask.add_url_rule" title="flask.Flask.add_url_rule"><tt class="xref py py-meth docutils literal"><span class="pre">add_url_rule()</span></tt></a> by prefixing a string with the project +name and a dot, and by wrapping <cite>view_func</cite> in a <cite>LazyView</cite> as needed:</p> +<div class="highlight-python"><div class="highlight"><pre><span class="k">def</span> <span class="nf">url</span><span class="p">(</span><span class="n">url_rule</span><span class="p">,</span> <span class="n">import_name</span><span class="p">,</span> <span class="o">**</span><span class="n">options</span><span class="p">):</span> + <span class="n">view</span> <span class="o">=</span> <span class="n">LazyView</span><span class="p">(</span><span class="s">'yourapplication.'</span> <span class="o">+</span> <span class="n">import_name</span><span class="p">)</span> + <span class="n">app</span><span class="o">.</span><span class="n">add_url_rule</span><span class="p">(</span><span class="n">url_rule</span><span class="p">,</span> <span class="n">view_func</span><span class="o">=</span><span class="n">view</span><span class="p">,</span> <span class="o">**</span><span class="n">options</span><span class="p">)</span> + +<span class="n">url</span><span class="p">(</span><span class="s">'/'</span><span class="p">,</span> <span class="s">'views.index'</span><span class="p">)</span> +<span class="n">url</span><span class="p">(</span><span class="s">'/user/<username>'</span><span class="p">,</span> <span class="s">'views.user'</span><span class="p">)</span> +</pre></div> +</div> +<p>One thing to keep in mind is that before and after request handlers have +to be in a file that is imported upfront to work properly on the first +request. The same goes for any kind of remaining decorator.</p> +</div> +</div> + + + </div> + </div> + </div> + <div class="sphinxsidebar"> + <div class="sphinxsidebarwrapper"><p class="logo"><a href="../index.html"> + <img class="logo" src="../_static/flask.png" alt="Logo"/> +</a></p> + <h3><a href="../index.html">Table Of Contents</a></h3> + <ul> +<li><a class="reference internal" href="#">Lazily Loading Views</a><ul> +<li><a class="reference internal" href="#converting-to-centralized-url-map">Converting to Centralized URL Map</a></li> +<li><a class="reference internal" href="#loading-late">Loading Late</a></li> +</ul> +</li> +</ul> +<h3>Related Topics</h3> +<ul> + <li><a href="../index.html">Documentation overview</a><ul> + <li><a href="index.html">Patterns for Flask</a><ul> + <li>Previous: <a href="errorpages.html" title="previous chapter">Custom Error Pages</a></li> + <li>Next: <a href="mongokit.html" title="next chapter">MongoKit in Flask</a></li> + </ul></li> + </ul></li> +</ul> + <h3>This Page</h3> + <ul class="this-page-menu"> + <li><a href="../_sources/patterns/lazyloading.txt" + rel="nofollow">Show Source</a></li> + </ul> +<div id="searchbox" style="display: none"> + <h3>Quick search</h3> + <form class="search" action="../search.html" method="get"> + <input type="text" name="q" /> + <input type="submit" value="Go" /> + <input type="hidden" name="check_keywords" value="yes" /> + <input type="hidden" name="area" value="default" /> + </form> + <p class="searchtip" style="font-size: 90%"> + Enter search terms or a module, class or function name. + </p> +</div> +<script type="text/javascript">$('#searchbox').show(0);</script> + </div> + </div> + <div class="clearer"></div> + </div> + <div class="footer"> + © Copyright 2010, Armin Ronacher. + Created using <a href="http://sphinx.pocoo.org/">Sphinx</a>. + </div> + </body> +</html>
\ No newline at end of file |