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<body>
<div class="document" id="paste-deployment">
<h1 class="title">Paste Deployment</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>Ian Bicking &lt;<a class="reference external" href="mailto:ianb&#37;&#52;&#48;colorstudy&#46;com">ianb<span>&#64;</span>colorstudy<span>&#46;</span>com</a>&gt;</td></tr>
</tbody>
</table>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#introduction" id="id3">Introduction</a></li>
<li><a class="reference internal" href="#status" id="id4">Status</a></li>
<li><a class="reference internal" href="#installation" id="id5">Installation</a></li>
<li><a class="reference internal" href="#from-the-user-perspective" id="id6">From the User Perspective</a><ul>
<li><a class="reference internal" href="#the-config-file" id="id7">The Config File</a></li>
</ul>
</li>
<li><a class="reference internal" href="#basic-usage" id="id8">Basic Usage</a></li>
<li><a class="reference internal" href="#config-uris" id="id9"><tt class="docutils literal">config:</tt> URIs</a><ul>
<li><a class="reference internal" href="#config-format" id="id10">Config Format</a></li>
<li><a class="reference internal" href="#applications" id="id11">Applications</a></li>
<li><a class="reference internal" href="#configuration" id="id12">Configuration</a></li>
<li><a class="reference internal" href="#global-configuration" id="id13">Global Configuration</a></li>
<li><a class="reference internal" href="#composite-applications" id="id14">Composite Applications</a></li>
<li><a class="reference internal" href="#other-objects" id="id15">Other Objects</a></li>
<li><a class="reference internal" href="#filter-composition" id="id16">Filter Composition</a></li>
<li><a class="reference internal" href="#getting-configuration" id="id17">Getting Configuration</a></li>
</ul>
</li>
<li><a class="reference internal" href="#egg-uris" id="id18"><tt class="docutils literal">egg:</tt> URIs</a></li>
<li><a class="reference internal" href="#defining-factories" id="id19">Defining Factories</a><ul>
<li><a class="reference internal" href="#paste-app-factory" id="id20"><tt class="docutils literal">paste.app_factory</tt></a></li>
<li><a class="reference internal" href="#paste-composite-factory" id="id21"><tt class="docutils literal">paste.composite_factory</tt></a></li>
<li><a class="reference internal" href="#paste-filter-factory" id="id22"><tt class="docutils literal">paste.filter_factory</tt></a></li>
<li><a class="reference internal" href="#paste-filter-app-factory" id="id23"><tt class="docutils literal">paste.filter_app_factory</tt></a></li>
<li><a class="reference internal" href="#paste-server-factory" id="id24"><tt class="docutils literal">paste.server_factory</tt></a></li>
<li><a class="reference internal" href="#paste-server-runner" id="id25"><tt class="docutils literal">paste.server_runner</tt></a></li>
</ul>
</li>
<li><a class="reference internal" href="#outstanding-issues" id="id26">Outstanding Issues</a></li>
</ul>
</div>
<p>Documents:</p>
<div class="system-message">
<p class="system-message-title">System Message: ERROR/3 (<tt class="docutils">docs/./index.txt</tt>, line 10)</p>
<p>Unknown directive type &quot;toctree&quot;.</p>
<pre class="literal-block">
.. toctree::
   :maxdepth: 1

   news
   modules/loadwsgi
   modules/config
   modules/converters
   license

</pre>
</div>
<!-- comment:
The names used in sections should be more concrete, and it should
be clearer that they are just arbitrary names. -->
<div class="section" id="introduction">
<h1>Introduction</h1>
<p>Paste Deployment is a system for finding and configuring WSGI
applications and servers.  For WSGI application consumers it provides
a single, simple function (<tt class="docutils literal">loadapp</tt>) for loading a WSGI application
from a configuration file or a Python Egg.  For WSGI application
providers it only asks for a single, simple entry point to your
application, so that application users don't need to be exposed to the
implementation details of your application.</p>
<p>The result is something a system administrator can install and manage
without knowing any Python, or the details of the WSGI application or
its container.</p>
<p>Paste Deployment currently does not require other parts of <a class="reference external" href="http://pythonpaste.org">Paste</a>, and is distributed as a separate package.</p>
<p>To see updates that have been made to Paste Deploy see the <a class="reference external" href="news.html">news file</a>.</p>
<p>Paste Deploy is released under the <a class="reference external" href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>.</p>
</div>
<div class="section" id="status">
<h1>Status</h1>
<p>Paste Deploy has passed version 1.0.  Paste Script is an actively
maintained project.  As of 1.0, we'll make a strong effort to maintain
backward compatibility (this actually started happening long before
1.0, but now it is explicit).  This will include deprecation warnings
when necessary.  Major changes will take place under new functions or
with new entry points.</p>
<p>Note that the most key aspect of Paste Deploy is the entry points it
defines (such as <tt class="docutils literal">paste.app_factory</tt>).  Paste Deploy is not the only
consumer of these entry points, and many extensions can best take
place by utilizing the entry points instead of using Paste Deploy
directly.  The entry points will not change; if changes are necessary,
new entry points will be defined.</p>
</div>
<div class="section" id="installation">
<h1>Installation</h1>
<p>First make sure you have either
<a class="reference external" href="http://peak.telecommunity.com/DevCenter/setuptools">setuptools</a> or its
modern replacement
<a class="reference external" href="http://pypi.python.org/pypi/distribute">distribute</a> installed.
For Python 3.x you need distribute as setuptools does not work on it.</p>
<p>Then you can install Paste Deployment using <a class="reference external" href="http://www.pip-installer.org/en/latest/installing.html">pip</a> by running:</p>
<pre class="literal-block">
$ sudo pip install PasteDeploy
</pre>
<p>If you want to track development, do:</p>
<pre class="literal-block">
$ hg clone http://bitbucket.org/ianb/pastedeploy
$ cd pastedeploy
$ sudo python setup.py develop
</pre>
<p>This will install the package globally, but will load the files in the
checkout.  You can also simply install <tt class="docutils literal"><span class="pre">PasteDeploy==dev</span></tt>.</p>
<p>For downloads and other information see the <a class="reference external" href="http://cheeseshop.python.org/pypi/PasteDeploy">Cheese Shop PasteDeploy
page</a>.</p>
<p>A complimentary package is <a class="reference external" href="/script/">Paste Script</a>.  To install
that, use <tt class="docutils literal">pip install PasteScript</tt> (or <tt class="docutils literal">pip install
<span class="pre">PasteScript==dev</span></tt>).</p>
</div>
<div class="section" id="from-the-user-perspective">
<h1>From the User Perspective</h1>
<p>In the following sections, the Python API for using Paste Deploy is
given.  This isn't what users will be using (but it is useful for
Python developers and useful for setting up tests fixtures).</p>
<p>The primary interaction with Paste Deploy is through its configuration
files.  The primary thing you want to do with a configuration file is
serve it.  To learn about serving configuration files, see <cite>the
``paster serve`</cite> command
&lt;<a class="reference external" href="http://pythonpaste.org/script/#paster-serve">http://pythonpaste.org/script/#paster-serve</a>&gt;`_.</p>
<div class="section" id="the-config-file">
<h2>The Config File</h2>
<p>A config file has different sections.  The only sections Paste Deploy
cares about have prefixes, like <tt class="docutils literal">app:main</tt> or <tt class="docutils literal">filter:errors</tt> --
the part after the <tt class="docutils literal">:</tt> is the &quot;name&quot; of the section, and the part
before gives the &quot;type&quot;.  Other sections are ignored.</p>
<p>The format is a simple <a class="reference external" href="http://en.wikipedia.org/wiki/INI_file">INI format</a>: <tt class="docutils literal">name = value</tt>.  You can
extend the value by indenting subsequent lines.  <tt class="docutils literal">#</tt> is a comment.</p>
<p>Typically you have one or two sections, named &quot;main&quot;: an application
section (<tt class="docutils literal">[app:main]</tt>) and a server section (<tt class="docutils literal">[server:main]</tt>).
<tt class="docutils literal"><span class="pre">[composite:...]</span></tt> signifies something that dispatches to multiple
applications (example below).</p>
<p>Here's a typical configuration file that also shows off mounting
multiple applications using <a class="reference external" href="http://pythonpaste.org/module-paste.urlmap.html">paste.urlmap</a>:</p>
<pre class="literal-block">
[composite:main]
use = egg:Paste#urlmap
/ = home
/blog = blog
/wiki = wiki
/cms = config:cms.ini

[app:home]
use = egg:Paste#static
document_root = %(here)s/htdocs

[filter-app:blog]
use = egg:Authentication#auth
next = blogapp
roles = admin
htpasswd = /home/me/users.htpasswd

[app:blogapp]
use = egg:BlogApp
database = sqlite:/home/me/blog.db

[app:wiki]
use = call:mywiki.main:application
database = sqlite:/home/me/wiki.db
</pre>
<p>I'll explain each section in detail now:</p>
<pre class="literal-block">
[composite:main]
use = egg:Paste#urlmap
/ = home
/blog = blog
/cms = config:cms.ini
</pre>
<p>That this is a <tt class="docutils literal">composite</tt> section means it dispatches the request
to other applications.  <tt class="docutils literal">use = egg:Paste#urlmap</tt> means to use the
composite application named <tt class="docutils literal">urlmap</tt> from the <tt class="docutils literal">Paste</tt> package.
<tt class="docutils literal">urlmap</tt> is a particularly common composite application -- it uses a
path prefix to map your request to another application.  These are
the applications like &quot;home&quot;, &quot;blog&quot;, &quot;wiki&quot; and &quot;config:cms.ini&quot;.  The last
one just refers to another file <tt class="docutils literal">cms.ini</tt> in the same directory.</p>
<p>Next up:</p>
<pre class="literal-block">
[app:home]
use = egg:Paste#static
document_root = %(here)s/htdocs
</pre>
<p><tt class="docutils literal">egg:Paste#static</tt> is another simple application, in this case it
just serves up non-dynamic files.  It takes one bit of configuration:
<tt class="docutils literal">document_root</tt>.  You can use variable substitution, which will pull
variables from the section <tt class="docutils literal">[DEFAULT]</tt> (case sensitive!) with
markers like <tt class="docutils literal">%(var_name)s</tt>.  The special variable <tt class="docutils literal">%(here)s</tt> is
the directory containing the configuration file; you should use that
in lieu of relative filenames (which depend on the current directory,
which can change depending how the server is run).</p>
<p>Then:</p>
<pre class="literal-block">
[filter-app:blog]
use = egg:Authentication#auth
next = blogapp
roles = admin
htpasswd = /home/me/users.htpasswd

[app:blogapp]
use = egg:BlogApp
database = sqlite:/home/me/blog.db
</pre>
<p>The <tt class="docutils literal"><span class="pre">[filter-app:blog]</span></tt> section means that you want an application
with a filter applied.  The application being filtered is indicated
with <tt class="docutils literal">next</tt> (which refers to the next section).  The
<tt class="docutils literal">egg:Authentication#auth</tt> filter doesn't actually exist, but one
could imagine it logs people in and checks permissions.</p>
<p>That last section is just a reference to an application that you
probably installed with <tt class="docutils literal">pip install BlogApp</tt>, and one bit of
configuration you passed to it (<tt class="docutils literal">database</tt>).</p>
<p>Lastly:</p>
<pre class="literal-block">
[app:wiki]
use = call:mywiki.main:application
database = sqlite:/home/me/wiki.db
</pre>
<p>This section is similar to the previous one, with one important difference.
Instead of an entry point in an egg, it refers directly to the <tt class="docutils literal">application</tt>
variable in the <tt class="docutils literal">mywiki.main</tt> module. The reference consist of two parts,
separated by a colon. The left part is the full name of the module and the
right part is the path to the variable, as a Python expression relative to the
containing module.</p>
<p>So, that's most of the features you'll use.</p>
</div>
</div>
<div class="section" id="basic-usage">
<h1>Basic Usage</h1>
<p>The basic way you'll use Paste Deployment is to load <a class="reference external" href="http://www.python.org/peps/pep-3333.html">WSGI</a> applications.  Many
Python frameworks now support WSGI, so applications written for these
frameworks should be usable.</p>
<p>The primary function is <tt class="docutils literal">paste.deploy.loadapp</tt>.  This loads an
application given a URI.  You can use it like:</p>
<pre class="literal-block">
from paste.deploy import loadapp
wsgi_app = loadapp('config:/path/to/config.ini')
</pre>
<p>There's two URI formats currently supported: <tt class="docutils literal">config:</tt> and <tt class="docutils literal">egg:</tt>.</p>
</div>
<div class="section" id="config-uris">
<h1><tt class="docutils literal">config:</tt> URIs</h1>
<p>URIs that being with <tt class="docutils literal">config:</tt> refer to configuration files.  These
filenames can be relative if you pass the <tt class="docutils literal">relative_to</tt> keyword
argument to <tt class="docutils literal">loadapp()</tt>.</p>
<div class="note">
<p class="first admonition-title">Note</p>
<p class="last">Filenames are never considered relative to the current working
directory, as that is a unpredictable location.  Generally when
a URI has a context it will be seen as relative to that context;
for example, if you have a <tt class="docutils literal">config:</tt> URI inside another
configuration file, the path is considered relative to the
directory that contains that configuration file.</p>
</div>
<div class="section" id="config-format">
<h2>Config Format</h2>
<p>Configuration files are in the INI format.  This is a simple format
that looks like:</p>
<pre class="literal-block">
[section_name]
key = value
another key = a long value
    that extends over multiple lines
</pre>
<p>All values are strings (no quoting is necessary).  The keys and
section names are case-sensitive, and may contain punctuation and
spaces (though both keys and values are stripped of leading and
trailing whitespace).  Lines can be continued with leading whitespace.</p>
<p>Lines beginning with <tt class="docutils literal">#</tt> (preferred) or <tt class="docutils literal">;</tt> are considered
comments.</p>
</div>
<div class="section" id="applications">
<h2>Applications</h2>
<p>You can define multiple applications in a single file; each
application goes in its own section.  Even if you have just one
application, you must put it in a section.</p>
<p>Each section name defining an application should be prefixed with
<tt class="docutils literal">app:</tt>.  The &quot;main&quot; section (when just defining one application)
would go in <tt class="docutils literal">[app:main]</tt> or just <tt class="docutils literal">[app]</tt>.</p>
<p>There's two ways to indicate the Python code for the application.  The
first is to refer to another URI or name:</p>
<pre class="literal-block">
[app:myapp]
use = config:another_config_file.ini#app_name

# or any URI:
[app:myotherapp]
use = egg:MyApp

# or a callable from a module:
[app:mythirdapp]
use = call:my.project:myapplication

# or even another section:
[app:mylastapp]
use = myotherapp
</pre>
<p>It would seem at first that this was pointless; just a way to point to
another location.  However, in addition to loading the application
from that location, you can also add or change the configuration.</p>
<p>The other way to define an application is to point exactly to some
Python code:</p>
<pre class="literal-block">
[app:myapp]
paste.app_factory = myapp.modulename:app_factory
</pre>
<p>You must give an explicit <em>protocol</em> (in this case
<tt class="docutils literal">paste.app_factory</tt>), and the value is something to import.  In
this case the module <tt class="docutils literal">myapp.modulename</tt> is loaded, and the
<tt class="docutils literal">app_factory</tt> object retrieved from it.</p>
<p>See <a class="reference internal" href="#defining-factories">Defining Factories</a> for more about the protocols.</p>
</div>
<div class="section" id="configuration">
<h2>Configuration</h2>
<p>Configuration is done through keys besides <tt class="docutils literal">use</tt> (or the protocol
names).  Any other keys found in the section will be passed as keyword
arguments to the factory.  This might look like:</p>
<pre class="literal-block">
[app:blog]
use = egg:MyBlog
database = mysql://localhost/blogdb
blogname = This Is My Blog!
</pre>
<p>You can override these in other sections, like:</p>
<pre class="literal-block">
[app:otherblog]
use = blog
blogname = The other face of my blog
</pre>
<p>This way some settings could be defined in a generic configuration
file (if you have <tt class="docutils literal">use = config:other_config_file</tt>) or you can
publish multiple (more specialized) applications just by adding a
section.</p>
</div>
<div class="section" id="global-configuration">
<h2>Global Configuration</h2>
<p>Often many applications share the same configuration.  While you can
do that a bit by using other config sections and overriding values,
often you want that done for a bunch of disparate configuration
values.  And typically applications can't take &quot;extra&quot; configuration
parameters; with global configuration you do something equivalent to
&quot;if this application wants to know the admin email, this is it&quot;.</p>
<p>Applications are passed the global configuration separately, so they
must specifically pull values out of it; typically the global
configuration serves as the basis for defaults when no local
configuration is passed in.</p>
<p>Global configuration to apply to every application defined in a file
should go in a special section named <tt class="docutils literal">[DEFAULT]</tt>.  You can override
global configuration locally like:</p>
<pre class="literal-block">
[DEFAULT]
admin_email = webmaster&#64;example.com

[app:main]
use = ...
set admin_email = bob&#64;example.com
</pre>
<p>That is, by using <tt class="docutils literal">set</tt> in front of the key.</p>
</div>
<div class="section" id="composite-applications">
<h2>Composite Applications</h2>
<p>&quot;Composite&quot; applications are things that act like applications, but
are made up of other applications.  One example would be a URL mapper,
where you mount applications at different URL paths.  This might look
like:</p>
<pre class="literal-block">
[composite:main]
use = egg:Paste#urlmap
/ = mainapp
/files = staticapp

[app:mainapp]
use = egg:MyApp

[app:staticapp]
use = egg:Paste#static
document_root = /path/to/docroot
</pre>
<p>The composite application &quot;main&quot; is just like any other application
from the outside (you load it with <tt class="docutils literal">loadapp</tt> for instance), but it
has access to other applications defined in the configuration file.</p>
</div>
<div class="section" id="other-objects">
<h2>Other Objects</h2>
<p>In addition to sections with <tt class="docutils literal">app:</tt>, you can define filters and
servers in a configuration file, with <tt class="docutils literal">server:</tt> and <tt class="docutils literal">filter:</tt>
prefixes.  You load these with <tt class="docutils literal">loadserver</tt> and <tt class="docutils literal">loadfilter</tt>.  The
configuration works just the same; you just get back different kinds
of objects.</p>
</div>
<div class="section" id="filter-composition">
<h2>Filter Composition</h2>
<p>There are several ways to apply filters to applications.  It mostly
depends on how many filters, and in what order you want to apply them.</p>
<p>The first way is to use the <tt class="docutils literal"><span class="pre">filter-with</span></tt> setting, like:</p>
<pre class="literal-block">
[app:main]
use = egg:MyEgg
filter-with = printdebug

[filter:printdebug]
use = egg:Paste#printdebug
# and you could have another filter-with here, and so on...
</pre>
<p>Also, two special section types exist to apply filters to your
applications: <tt class="docutils literal"><span class="pre">[filter-app:...]</span></tt> and <tt class="docutils literal"><span class="pre">[pipeline:...]</span></tt>.  Both of
these sections define applications, and so can be used wherever an
application is needed.</p>
<p><tt class="docutils literal"><span class="pre">filter-app</span></tt> defines a filter (just like you would in a
<tt class="docutils literal"><span class="pre">[filter:...]</span></tt> section), and then a special key <tt class="docutils literal">next</tt> which
points to the application to apply the filter to.</p>
<p><tt class="docutils literal">pipeline:</tt> is used when you need apply a number of filters.  It
takes <em>one</em> configuration key <tt class="docutils literal">pipeline</tt> (plus any global
configuration overrides you want).  <tt class="docutils literal">pipeline</tt> is a list of filters
ended by an application, like:</p>
<pre class="literal-block">
[pipeline:main]
pipeline = filter1 egg:FilterEgg#filter2 filter3 app

[filter:filter1]
...
</pre>
</div>
<div class="section" id="getting-configuration">
<h2>Getting Configuration</h2>
<p>If you want to get the configuration without creating the application,
you can use the <tt class="docutils literal">appconfig(uri)</tt> function, which is just like the
<tt class="docutils literal">loadapp()</tt> function except it returns the configuration that would
be used, as a dictionary.  Both global and local configuration is
combined into a single dictionary, but you can look at just one or the
other with the attributes <tt class="docutils literal">.local_conf</tt> and <tt class="docutils literal">.global_conf</tt>.</p>
</div>
</div>
<div class="section" id="egg-uris">
<h1><tt class="docutils literal">egg:</tt> URIs</h1>
<div class="system-message">
<p class="system-message-title">System Message: WARNING/2 (<tt class="docutils">docs/./index.txt</tt>, line 2); <em><a href="#id2">backlink</a></em></p>
Duplicate explicit target name: &quot;distribute&quot;.</div>
<p><a class="reference external" href="http://peak.telecommunity.com/DevCenter/PythonEggs">Python Eggs</a>
are a distribution and installation format produced by <a class="reference external" href="http://peak.telecommunity.com/DevCenter/setuptools">setuptools</a> and
<a class="reference external" href="http://packages.python.org/distribute/">distribute</a> that adds metadata to a
normal Python package (among other things).</p>
<p>You don't need to understand a whole lot about Eggs to use them.  If
you have a <a class="reference external" href="http://python.org/doc/current/lib/module-distutils.html">distutils</a>
<tt class="docutils literal">setup.py</tt> script, just change:</p>
<pre class="literal-block">
from distutils.core import setup
</pre>
<p>to:</p>
<pre class="literal-block">
from setuptools import setup
</pre>
<p>Now when you install the package it will be installed as an egg.</p>
<p>The first important part about an Egg is that it has a
<em>specification</em>.  This is formed from the name of your distribution
(the <tt class="docutils literal">name</tt> keyword argument to <tt class="docutils literal">setup()</tt>), and you can specify a
specific version.  So you can have an egg named <tt class="docutils literal">MyApp</tt>, or
<tt class="docutils literal"><span class="pre">MyApp==0.1</span></tt> to specify a specific version.</p>
<p>The second is <em>entry points</em>.  These are references to Python objects
in your packages that are named and have a specific protocol.
&quot;Protocol&quot; here is just a way of saying that we will call them with
certain arguments, and expect a specific return value.  We'll talk
more about the protocols <a class="reference internal" href="#defining-factories">later</a>.</p>
<p>The important part here is how we define entry points.  You'll add an
argument to <tt class="docutils literal">setup()</tt> like:</p>
<pre class="literal-block">
setup(
    name='MyApp',
    ...
    entry_points={
        'paste.app_factory': [
            'main=myapp.mymodule:app_factory',
            'ob2=myapp.mymodule:ob_factory'],
        },
    )
</pre>
<p>This defines two applications named <tt class="docutils literal">main</tt> and <tt class="docutils literal">ob2</tt>.  You can
then refer to these by <tt class="docutils literal">egg:MyApp#main</tt> (or just <tt class="docutils literal">egg:MyApp</tt>,
since <tt class="docutils literal">main</tt> is the default) and <tt class="docutils literal">egg:MyApp#ob2</tt>.</p>
<p>The values are instructions for importing the objects.  <tt class="docutils literal">main</tt> is
located in the <tt class="docutils literal">myapp.mymodule</tt> module, in an object named
<tt class="docutils literal">app_factory</tt>.</p>
<p>There's no way to add configuration to objects imported as Eggs.</p>
</div>
<div class="section" id="defining-factories">
<h1>Defining Factories</h1>
<p>This lets you point to factories (that obey the specific protocols we
mentioned).  But that's not much use unless you can create factories
for your applications.</p>
<p>There's a few protocols: <tt class="docutils literal">paste.app_factory</tt>,
<tt class="docutils literal">paste.composite_factory</tt>, <tt class="docutils literal">paste.filter_factory</tt>, and lastly
<tt class="docutils literal">paste.server_factory</tt>.  Each of these expects a callable (like a
function, method, or class).</p>
<div class="section" id="paste-app-factory">
<h2><tt class="docutils literal">paste.app_factory</tt></h2>
<p>The application is the most common.  You define one like:</p>
<pre class="literal-block">
def app_factory(global_config, **local_conf):
    return wsgi_app
</pre>
<p>The <tt class="docutils literal">global_config</tt> is a dictionary, and local configuration is
passed as keyword arguments.  The function returns a WSGI application.</p>
</div>
<div class="section" id="paste-composite-factory">
<h2><tt class="docutils literal">paste.composite_factory</tt></h2>
<p>Composites are just slightly more complex:</p>
<pre class="literal-block">
def composite_factory(loader, global_config, **local_conf):
    return wsgi_app
</pre>
<p>The <tt class="docutils literal">loader</tt> argument is an object that has a couple interesting
methods.  <tt class="docutils literal">get_app(name_or_uri, global_conf=None)</tt> return a WSGI
application with the given name.  <tt class="docutils literal">get_filter</tt> and <tt class="docutils literal">get_server</tt>
work the same way.</p>
<p>A more interesting example might be a composite factory that does
something.  For instance, consider a &quot;pipeline&quot; application:</p>
<pre class="literal-block">
def pipeline_factory(loader, global_config, pipeline):
    # space-separated list of filter and app names:
    pipeline = pipeline.split()
    filters = [loader.get_filter(n) for n in pipeline[:-1]]
    app = loader.get_app(pipeline[-1])
    filters.reverse() # apply in reverse order!
    for filter in filters:
        app = filter(app)
    return app
</pre>
<p>Then we use it like:</p>
<pre class="literal-block">
[composite:main]
use = &lt;pipeline_factory_uri&gt;
pipeline = egg:Paste#printdebug session myapp

[filter:session]
use = egg:Paste#session
store = memory

[app:myapp]
use = egg:MyApp
</pre>
</div>
<div class="section" id="paste-filter-factory">
<h2><tt class="docutils literal">paste.filter_factory</tt></h2>
<p>Filter factories are just like app factories (same signature), except
they return filters.  Filters are callables that take a WSGI
application as the only argument, and return a &quot;filtered&quot; version of
that application.</p>
<p>Here's an example of a filter that checks that the <tt class="docutils literal">REMOTE_USER</tt> CGI
variable is set, creating a really simple authentication filter:</p>
<pre class="literal-block">
def auth_filter_factory(global_conf, req_usernames):
    # space-separated list of usernames:
    req_usernames = req_usernames.split()
    def filter(app):
        return AuthFilter(app, req_usernames)
    return filter

class AuthFilter(object):
    def __init__(self, app, req_usernames):
        self.app = app
        self.req_usernames = req_usernames

    def __call__(self, environ, start_response):
        if environ.get('REMOTE_USER') in self.req_usernames:
            return self.app(environ, start_response)
        start_response(
            '403 Forbidden', [('Content-type', 'text/html')])
        return ['You are forbidden to view this resource']
</pre>
</div>
<div class="section" id="paste-filter-app-factory">
<h2><tt class="docutils literal">paste.filter_app_factory</tt></h2>
<p>This is very similar to <tt class="docutils literal">paste.filter_factory</tt>, except that it also
takes a <tt class="docutils literal">wsgi_app</tt> argument, and returns a WSGI application.  So if
you changed the above example to:</p>
<pre class="literal-block">
class AuthFilter(object):
    def __init__(self, app, global_conf, req_usernames):
        ....
</pre>
<p>Then <tt class="docutils literal">AuthFilter</tt> would serve as a filter_app_factory
(<tt class="docutils literal">req_usernames</tt> is a required local configuration key in this
case).</p>
</div>
<div class="section" id="paste-server-factory">
<h2><tt class="docutils literal">paste.server_factory</tt></h2>
<p>This takes the same signature as applications and filters, but returns
a server.</p>
<p>A server is a callable that takes a single argument, a WSGI
application.  It then serves the application.</p>
<p>An example might look like:</p>
<pre class="literal-block">
def server_factory(global_conf, host, port):
    port = int(port)
    def serve(app):
        s = Server(app, host=host, port=port)
        s.serve_forever()
    return serve
</pre>
<p>The implementation of <tt class="docutils literal">Server</tt> is left to the user.</p>
</div>
<div class="section" id="paste-server-runner">
<h2><tt class="docutils literal">paste.server_runner</tt></h2>
<p>Like <tt class="docutils literal">paste.server_factory</tt>, except <tt class="docutils literal">wsgi_app</tt> is passed as the
first argument, and the server should run immediately.</p>
</div>
</div>
<div class="section" id="outstanding-issues">
<h1>Outstanding Issues</h1>
<ul>
<li><p class="first">Should there be a &quot;default&quot; protocol for each type of object?  Since
there's currently only one protocol, it seems like it makes sense
(in the future there could be multiple).  Except that
<tt class="docutils literal">paste.app_factory</tt> and <tt class="docutils literal">paste.composite_factory</tt> overlap
considerably.</p>
</li>
<li><p class="first">ConfigParser's INI parsing is kind of annoying.  I'd like it both
more constrained and less constrained.  Some parts are sloppy (like
the way it interprets <tt class="docutils literal">[DEFAULT]</tt>).</p>
</li>
<li><p class="first"><tt class="docutils literal">config:</tt> URLs should be potentially relative to other locations,
e.g., <tt class="docutils literal"><span class="pre">config:$docroot/...</span></tt>.  Maybe using variables from
<tt class="docutils literal">global_conf</tt>?</p>
</li>
<li><p class="first">Should other variables have access to <tt class="docutils literal">global_conf</tt>?</p>
</li>
<li><p class="first">Should objects be Python-syntax, instead of always strings?  Lots of
code isn't usable with Python strings without a thin wrapper to
translate objects into their proper types.</p>
</li>
<li><p class="first">Some short-form for a filter/app, where the filter refers to the
&quot;next app&quot;.  Maybe like:</p>
<pre class="literal-block">
[app-filter:app_name]
use = egg:...
next = next_app

[app:next_app]
...
</pre>
</li>
</ul>
</div>
</div>
</body>
</html>
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