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.. _startup_chapter:
Startup
=======
When you cause a :app:`Pyramid` application to start up in a console window,
you'll see something much like this show up on the console:
.. code-block:: text
$ pserve development.ini
Starting server in PID 16601.
serving on 0.0.0.0:6543 view at http://127.0.0.1:6543
This chapter explains what happens between the time you press the "Return"
key on your keyboard after typing ``pserve development.ini``
and the time the line ``serving on 0.0.0.0:6543 ...`` is output to your
console.
.. index::
single: startup process
pair: settings; .ini
The Startup Process
-------------------
The easiest and best-documented way to start and serve a :app:`Pyramid`
application is to use the ``pserve`` command against a :term:`PasteDeploy`
``.ini`` file. This uses the ``.ini`` file to infer settings and starts a
server listening on a port. For the purposes of this discussion, we'll
assume that you are using this command to run your :app:`Pyramid`
application.
Here's a high-level time-ordered overview of what happens when you press
``return`` after running ``pserve development.ini``.
#. The ``pserve`` command is invoked under your shell with the argument
``development.ini``. As a result, Pyramid recognizes that it is meant to
begin to run and serve an application using the information contained
within the ``development.ini`` file.
#. The framework finds a section named either ``[app:main]``,
``[pipeline:main]``, or ``[composite:main]`` in the ``.ini`` file. This
section represents the configuration of a :term:`WSGI` application that
will be served. If you're using a simple application (e.g.
``[app:main]``), the application's ``paste.app_factory`` :term:`entry
point` will be named on the ``use=`` line within the section's
configuration. If, instead of a simple application, you're using a WSGI
:term:`pipeline` (e.g. a ``[pipeline:main]`` section), the application
named on the "last" element will refer to your :app:`Pyramid` application.
If instead of a simple application or a pipeline, you're using a
"composite" (e.g. ``[composite:main]``), refer to the documentation for
that particular composite to understand how to make it refer to your
:app:`Pyramid` application. In most cases, a Pyramid application built
from a scaffold will have a single ``[app:main]`` section in it, and this
will be the application served.
#. The framework finds all :mod:`logging` related configuration in the
``.ini`` file and uses it to configure the Python standard library logging
system for this application. See :ref:`logging_config` for more
information.
#. The application's *constructor* named by the entry point reference on the
``use=`` line of the section representing your :app:`Pyramid` application
is passed the key/value parameters mentioned within the section in which
it's defined. The constructor is meant to return a :term:`router`
instance, which is a :term:`WSGI` application.
For :app:`Pyramid` applications, the constructor will be a function named
``main`` in the ``__init__.py`` file within the :term:`package` in which
your application lives. If this function succeeds, it will return a
:app:`Pyramid` :term:`router` instance. Here's the contents of an example
``__init__.py`` module:
.. literalinclude:: MyProject/myproject/__init__.py
:language: python
:linenos:
Note that the constructor function accepts a ``global_config`` argument,
which is a dictionary of key/value pairs mentioned in the ``[DEFAULT]``
section of an ``.ini`` file
(if :ref:`[DEFAULT] <defaults_section_of_pastedeploy_file>` is present).
It also accepts a ``**settings`` argument, which collects
another set of arbitrary key/value pairs. The arbitrary key/value pairs
received by this function in ``**settings`` will be composed of all the
key/value pairs that are present in the ``[app:main]`` section (except for
the ``use=`` setting) when this function is called by when you run
``pserve``.
Our generated ``development.ini`` file looks like so:
.. literalinclude:: MyProject/development.ini
:language: ini
:linenos:
In this case, the ``myproject.__init__:main`` function referred to by the
entry point URI ``egg:MyProject`` (see :ref:`MyProject_ini` for more
information about entry point URIs, and how they relate to callables),
will receive the key/value pairs ``{'pyramid.reload_templates':'true',
'pyramid.debug_authorization':'false', 'pyramid.debug_notfound':'false',
'pyramid.debug_routematch':'false', 'pyramid.debug_templates':'true',
'pyramid.default_locale_name':'en'}``. See :ref:`environment_chapter` for
the meanings of these keys.
#. The ``main`` function first constructs a
:class:`~pyramid.config.Configurator` instance, passing the ``settings``
dictionary captured via the ``**settings`` kwarg as its ``settings``
argument.
The ``settings`` dictionary contains all the options in the ``[app:main]``
section of our .ini file except the ``use`` option (which is internal to
PasteDeploy) such as ``pyramid.reload_templates``,
``pyramid.debug_authorization``, etc.
#. The ``main`` function then calls various methods on the instance of the
class :class:`~pyramid.config.Configurator` created in the previous step.
The intent of calling these methods is to populate an
:term:`application registry`, which represents the :app:`Pyramid`
configuration related to the application.
#. The :meth:`~pyramid.config.Configurator.make_wsgi_app` method is called.
The result is a :term:`router` instance. The router is associated with
the :term:`application registry` implied by the configurator previously
populated by other methods run against the Configurator. The router is a
WSGI application.
#. An :class:`~pyramid.events.ApplicationCreated` event is emitted (see
:ref:`events_chapter` for more information about events).
#. Assuming there were no errors, the ``main`` function in ``myproject``
returns the router instance created by
:meth:`pyramid.config.Configurator.make_wsgi_app` back to ``pserve``. As
far as ``pserve`` is concerned, it is "just another WSGI application".
#. ``pserve`` starts the WSGI *server* defined within the ``[server:main]``
section. In our case, this is the Waitress server (``use =
egg:waitress#main``), and it will listen on all interfaces (``host =
0.0.0.0``), on port number 6543 (``port = 6543``). The server code itself
is what prints ``serving on 0.0.0.0:6543 view at http://127.0.0.1:6543``.
The server serves the application, and the application is running, waiting
to receive requests.
.. seealso::
Logging configuration is described in the :ref:`logging_chapter`
chapter. There, in :ref:`request_logging_with_pastes_translogger`,
you will also find an example of how to configure
:term:`middleware` to add pre-packaged functionality to your
application.
.. index::
pair: settings; deployment
single: custom settings
.. _deployment_settings:
Deployment Settings
-------------------
Note that an augmented version of the values passed as ``**settings`` to the
:class:`~pyramid.config.Configurator` constructor will be available in
:app:`Pyramid` :term:`view callable` code as ``request.registry.settings``.
You can create objects you wish to access later from view code, and put them
into the dictionary you pass to the configurator as ``settings``. They will
then be present in the ``request.registry.settings`` dictionary at
application runtime.
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