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.. _paste_chapter:
PasteDeploy Configuration Files
===============================
Packages generated via a :term:`scaffold` make use of a system created by Ian
Bicking named :term:`PasteDeploy`. PasteDeploy defines a way to declare
:term:`WSGI` application configuration in an ``.ini`` file.
Pyramid uses this configuration file format in input to its :term:`WSGI`
server runner ``pserve``, as well as other commands such as ``pviews``,
``pshell``, ``proutes``, and ``ptweens``.
PasteDeploy is not a particularly integral part of Pyramid. It's possible to
create a Pyramid application which does not use PasteDeploy at all. We show
a Pyramid application that doesn't use PasteDeploy in
:ref:`firstapp_chapter`. However, all Pyramid scaffolds render PasteDeploy
configuration files, to provide new developers with a standardized way of
setting deployment values, and to provide new users with a standardized way
of starting, stopping, and debugging an application.
This chapter is not a replacement for documentation about PasteDeploy; it
only contextualizes the use of PasteDeploy within Pyramid. For detailed
documentation, see http://pythonpaste.org.
PasteDeploy
-----------
:term:`PasteDeploy` is the system that Pyramid uses to allow
:term:`deployment settings` to be spelled using an ``.ini`` configuration
file format. It also allows the ``pserve`` command to work. Its
configuration format provides a convenient place to define application
:term:`deployment settings` and WSGI server settings, and its server runner
allows you to stop and start a Pyramid application easily.
.. _pastedeploy_entry_points:
Entry Points and PasteDeploy ``.ini`` Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the :ref:`project_narr` chapter, we breezed over the meaning of a
configuration line in the ``deployment.ini`` file. This was the ``use =
egg:MyProject`` line in the ``[app:main]`` section. We breezed over it
because it's pretty confusing and "too much information" for an introduction
to the system. We'll try to give it a bit of attention here. Let's see the
config file again:
.. literalinclude:: MyProject/development.ini
:language: ini
:linenos:
The line in ``[app:main]`` above that says ``use = egg:MyProject`` is
actually shorthand for a longer spelling: ``use = egg:MyProject#main``. The
``#main`` part is omitted for brevity, as ``#main`` is a default defined by
PasteDeploy. ``egg:MyProject#main`` is a string which has meaning to
PasteDeploy. It points at a :term:`setuptools` :term:`entry point` named
``main`` defined in the ``MyProject`` project.
Take a look at the generated ``setup.py`` file for this project.
.. literalinclude:: MyProject/setup.py
:language: python
:linenos:
Note that ``entry_points`` is assigned a string which
looks a lot like an ``.ini`` file. This string representation of an ``.ini``
file has a section named ``[paste.app_factory]``. Within this section, there
is a key named ``main`` (the entry point name) which has a value
``myproject:main``. The *key* ``main`` is what our ``egg:MyProject#main``
value of the ``use`` section in our config file is pointing at, although it
is actually shortened to ``egg:MyProject`` there. The value represents a
:term:`dotted Python name` path, which refers to a callable in our
``myproject`` package's ``__init__.py`` module.
The ``egg:`` prefix in ``egg:MyProject`` indicates that this is an entry
point *URI* specifier, where the "scheme" is "egg". An "egg" is created when
you run ``setup.py install`` or ``setup.py develop`` within your project.
In English, this entry point can thus be referred to as a "PasteDeploy
application factory in the ``MyProject`` project which has the entry point
named ``main`` where the entry point refers to a ``main`` function in the
``mypackage`` module". Indeed, if you open up the ``__init__.py`` module
generated within any scaffold-generated package, you'll see a ``main``
function. This is the function called by :term:`PasteDeploy` when the
``pserve`` command is invoked against our application. It accepts a global
configuration object and *returns* an instance of our application.
``[DEFAULTS]`` Section of a PasteDeploy ``.ini`` File
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
You can add a ``[DEFAULT]`` section to your PasteDeploy ``.ini`` file. Such
a section should consists of global parameters that are shared by all the
applications, servers and :term:`middleware` defined within the configuration
file. The values in a ``[DEFAULT]`` section will be passed to your
application's ``main`` function as ``global_config`` (see the reference to
the ``main`` function in :ref:`init_py`).
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