path: root/docs/narr/project.rst

.. _project_narr:

Creating a :mod:`repoze.bfg` Project
====================================

It's possible to create a :mod:`repoze.bfg` application completely
manually, but it's usually more convenient to use a template to
generate a basic :mod:`repoze.bfg` application structure.

:mod:`repoze.bfg` comes with templates that you can use to generate a
project.  Each template makes different configuration assumptions
about what type of application you're trying to construct.

These templates are rendered using the :term:`PasteDeploy` ``paster``
script, and so therefore they are often referred to as "paster
templates".

.. index::
   single: paster templates
   single: bfg_starter paster template
   single: bfg_zodb paster template
   single: bfg_alchemy paster template
   single: bfg_routesalchemy paster template

.. _additional_paster_templates:

Paster Templates Included with :mod:`repoze.bfg`
------------------------------------------------

The convenience ``paster`` templates included with :mod:`repoze.bfg`
differ from each other on two axes:

- the persistence mechanism they offer (no persistence mechanism,
  :term:`ZODB`, or :term:`SQLAlchemy`).

- the mechanism they use to map URLs to code (:term:`traversal` or
  :term:`URL dispatch`).

The included templates are these:

``bfg_starter``

  URL mapping via :term:`traversal` and no persistence mechanism.

``bfg_zodb``

  URL mapping via :term:`traversal` and persistence via :term:`ZODB`

``bfg_routesalchemy`` 

  URL mapping via :term:`URL dispatch` and persistence via
  :term:`SQLAlchemy`

``bfg_alchemy``

  URL mapping via :term:`traversal` and persistence va
  :term:`SQLAlchemy`

Each of these project templates uses :term:`ZCML` instead of
:term:`imperative configuration`.  Each also makes the assumption that
you want your code to live in a Python :term:`package`.  Even if your
application is extremely simple, it is useful to place code that
drives the application within a package, because a package is more
easily extended with new code.  An application that lives inside a
package can also be distributed more easily than one which does not
live within a package.

.. index::
   single: creating a project
   single: project

.. _creating_a_project:

Creating the Project
--------------------

In in :ref:`installing_chapter`, you created a virtual Python
environment via the ``virtualenv`` command.  To start a
:mod:`repoze.bfg` :term:`project`, use the ``paster`` facility
installed within the virtualenv.  In :ref:`installing_chapter` we
called the virtualenv directory ``bfgenv``; the following command
assumes that our current working directory is that directory.

We'll choose the ``bfg_starter`` template for this purpose.

.. code-block:: text

   $ bin/paster create -t bfg_starter

The above command uses the ``paster`` command to create a project
using the ``bfg_starter`` template.  The ``create`` version of paster
invokes the creation of a project from a template.  To use a different
template, such as ``bfg_routesalchemy``, you'd just change the last
argument.  For example:

.. code-block:: text

   $ bin/paster create -t bfg_routesalchemy

``paster create`` will ask you a single question: the *name* of the
project.  You should use a string without spaces and with only letters
in it.  Here's sample output from a run of ``paster create`` for a
project we name ``MyProject``:

.. code-block:: text

   $ bin/paster create -t bfg_starter
   Selected and implied templates:
     repoze.bfg#bfg  repoze.bfg starter project

   Enter project name: MyProject
   Variables:
     egg:      MyProject
     package:  myproject
     project:  MyProject
   Creating template bfg
   Creating directory ./MyProject
   # ... more output ...
   Running /Users/chrism/projects/repoze/bfg/bin/python setup.py egg_info

.. note:: You can skip the interrogative question about a project
   name during ``paster create`` by adding the project name to the
   command line, e.g. ``paster create -t bfg_starter MyProject``.

As a result of invoking the ``paster create`` command, a project is
created in a directory named ``MyProject``.  That directory is a
:term:`setuptools` :term:`project` directory from which a setuptools
:term:`distribution` can be created.  The ``setup.py`` file in that
directory can be used to distribute your application, or install your
application for deployment or development.

A sample :term:`PasteDeploy` ``.ini`` file named ``MyProject.ini``
will also be created in the project directory.  You will use this
``.ini`` file to configure a server, to run your application, and to
and debug your application.

The ``MyProject`` project directory contains an additional
subdirectory named ``myproject`` (note the case difference)
representing a Python :term:`package` which holds very simple
:mod:`repoze.bfg` sample code.  This is where you'll edit your
application's Python code and templates.

.. index::
   single: setup.py develop
   single: development install

Installing your Newly Created Project for Development
-----------------------------------------------------

Using the interpreter from the :term:`virtualenv` you create during
:ref:`installing_chapter`, invoke the following command when inside
the project directory.  The file named ``setup.py`` will be in the
root of the paster-generated project directory.  The ``python`` you're
invoking should be the one that lives in the ``bin`` directory of your
virtual Python environment.

.. code-block:: text

   $ ../bin/python setup.py develop

Elided output from a run of this command is shown below:

.. code-block:: text

   $ ../bin/python setup.py develop
   ...
   Finished processing dependencies for MyProject==0.1

This will install the :term:`distribution` representing your
application's into the interpreter's library set so it can be found
and run by :term:`PasteDeploy` via the command ``paster serve``.

.. index::
   single: running tests
   single: tests (running)

Running The Tests For Your Application
--------------------------------------

To run unit tests for your application, you should invoke them using
the ``python`` that lives in the ``bin`` directory of your virtualenv:

.. code-block:: text

   $ ../bin/python setup.py test -q

Here's sample output from a test run:

.. code-block:: text

   $ python setup.py test -q
   running test
   running egg_info
   writing requirements to MyProject.egg-info/requires.txt
   writing MyProject.egg-info/PKG-INFO
   writing top-level names to MyProject.egg-info/top_level.txt
   writing dependency_links to MyProject.egg-info/dependency_links.txt
   writing entry points to MyProject.egg-info/entry_points.txt
   reading manifest file 'MyProject.egg-info/SOURCES.txt'
   writing manifest file 'MyProject.egg-info/SOURCES.txt'
   running build_ext
   ..
   ----------------------------------------------------------------------
   Ran 1 test in 0.108s

   OK

The tests themselves are found in the ``tests.py`` module in your
``paster create`` -generated project.  Within a project generated by
the ``bfg_starter`` template, a single sample test exists.

.. index::
   single: interactive shell
   single: IPython
   single: paster bfgshell

The Interactive Shell
---------------------

Once you've installed your program for development using ``setup.py
develop``, you can use an interactive Python shell to examine your
:mod:`repoze.bfg` application :term:`model` and :term:`view` objects
from a Python prompt.  To do so, use the ``paster`` shell command with
the ``bfgshell`` argument:

The first argument to ``bfgshell`` is the path to your application's
``.ini`` file.  The second is the section name inside the ``.ini``
file which points to your *application* as opposed to any other
section within the ``.ini`` file.  For example, if your application
``.ini`` file might have a ``[app:main]`` section that looks like so:

.. code-block:: ini
   :linenos:

   [app:main]
   use = egg:MyProject#app
   reload_templates = true
   debug_authorization = false
   debug_notfound = false

If so, you can use the following command to invoke a debug shell using
the name ``main`` as a section name:

.. code-block::  text

   [chrism@vitaminf bfgshellenv]$ ../bin/paster --plugin=repoze.bfg bfgshell \
         MyProject.ini main
   Python 2.4.5 (#1, Aug 29 2008, 12:27:37) 
   [GCC 4.0.1 (Apple Inc. build 5465)] on darwin
   Type "help" for more information. "root" is the BFG app root object.
   >>> root
   <foo.models.MyModel object at 0x445270>

.. note:: You *might* get away without passing
          ``--plugin=repoze.bfg`` to the bfgshell command.

If you have `IPython <http://en.wikipedia.org/wiki/IPython>`_
installed in the interpreter you use to invoke the ``paster`` command,
the ``bfgshell`` command will use an IPython interactive shell instead
of a standard Python interpreter shell.  If you don't want this to
happen, even if you have IPython installed, you can pass the
``--disable-ipython`` flag to the ``bfgshell`` command to use a
standard Python interpreter shell unconditionally.

.. code-block::  text

   [chrism@vitaminf bfgshellenv]$ ../bin/paster --plugin=repoze.bfg bfgshell \
         --disable-ipython MyProject.ini main

You should always use a section name argument that refers to the
actual ``app`` section within the Paste configuration file that points
at your :mod:`repoze.bfg` application *without any middleware
wrapping*.  In particular, a section name is inappropriate as the
second argument to "bfgshell" if the configuration section it names is
a ``pipeline`` rather than an ``app``.  For example, if you have the
following ``.ini`` file content:

.. code-block:: ini
   :linenos:

   [app:myapp]
   use = egg:MyProject#app
   reload_templates = true
   debug_authorization = false
   debug_notfound = false

   [pipeline:main]
   pipeline = egg:repoze.tm2#tm
              myapp

The command you use to invoke the interactive shell should be:

.. code-block::  text

   [chrism@vitaminf bfgshellenv]$ ../bin/paster --plugin=repoze.bfg bfgshell \
         MyProject.ini myapp

If you use ``main`` as the section name argument instead of ``myapp``
against the above ``.ini`` file, an error will likely occur.  Use the
most specific reference to the application within the ``.ini`` file
possible as the section name argument.

Press ``Ctrl-D`` to exit the interactive shell (or ``Ctrl-Z`` on
Windows).

.. index::
   single: running an application
   single: paster serve
   single: reload
   single: startup
   single: mod_wsgi

Runnning The Project Application
--------------------------------

Once a project is installed for development, you can run the
application it represents using the ``paster serve`` command against
the generated configuration file.  In our case, this file is named
``MyProject.ini``:

.. code-block:: text

   $ ../bin/paster serve MyProject.ini

Here's sample output from a run of ``paster serve``:

.. code-block:: text

   $ ../bin/paster serve MyProject.ini
   Starting server in PID 16601.
   serving on 0.0.0.0:6543 view at http://127.0.0.1:6543

By default, :mod:`repoze.bfg` applications generated from a ``paster``
template will listen on TCP port 6543.

During development, it's often useful to run ``paster serve`` using
its ``--reload`` option.  When ``--reload`` is passed to ``paster
serve``, changes to any Python module your project uses will cause the
server to restart.  This typically makes development easier, as
changes to Python code made within a :mod:`repoze.bfg` application is
not put into effect until the server restarts.

For example:

.. code-block:: text

   $ ../bin/paster serve MyProject.ini --reload
   Starting subprocess with file monitor
   Starting server in PID 16601.
   serving on 0.0.0.0:6543 view at http://127.0.0.1:6543

For more detailed information about the startup process, see
:ref:`startup_chapter`.  For more information about environment
variables and configuration file settings that influence startup and
runtime behavior, see :ref:`environment_chapter`.

Using an Alternate WSGI Server
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The code generated by :mod:`repoze.bfg` ``paster`` templates assumes
that you will be using the ``paster serve`` command to start your
application while you do development.  However, ``paster serve`` is by
no means the only way to start up and serve a :mod:`repoze.bfg`
application.  As we saw in :ref:`configuration_narr`, ``paster serve``
needn't be invoked at all to run a :mod:`repoze.bfg` application.  The
use of ``paster serve`` to run a :mod:`repoze.bfg` application is
purely conventional based on the output of its ``paster`` templates.

Any :term:`WSGI` server is capable of running a :mod:`repoze.bfg`
application.  Some WSGI servers don't require the :term:`PasteDeploy`
framework's ``paster serve`` command to do server process management
at all.  Each :term:`WSGI` server has its own documentation about how
it creates a process to run an application, and there are many of
them, so we cannot provide the details for each here.  But the
concepts are largely the same, whatever server you happen to use.

One popular production alternative to a ``paster``-invoked server is
:term:`mod_wsgi`.  can also use :term:`mod_wsgi` to serve your
:mod:`repoze.bfg` application using the Apache web server rather than
any "pure-Python" server that is started as a result of ``paster
serve``.  See :ref:`modwsgi_tutorial` for details.  However, it is
usually easier to *develop* an application using a ``paster serve``
-invoked webserver, as exception and debugging output will be sent to
the console.

Viewing the Application
-----------------------

Once your application is running via ``paster serve``, you may visit
``http://localhost:6543/`` in your browser.  You will see something in
your browser like what is displayed in the following image:

.. image:: project.png

This is the page shown by default when you visit an unmodified
``paster create`` -generated ``bfg_starter`` application in a browser.

.. index::
   single: project structure

The Project Structure
---------------------

Our generated :mod:`repoze.bfg` ``bfg_starter`` application is a
setuptools :term:`project` (named ``MyProject``), which contains a
Python :term:`package` (which is *also* named ``myproject``, but
lowercased; the paster template generates a project which contains a
package that shares its name except for case).  All :mod:`repoze.bfg`
``paster`` -generated projects share a similar structure.

The ``MyProject`` project we've generated has the following directory
structure::

  MyProject/
  |-- CHANGES.txt
  |-- README.txt
  |-- myproject
  |   |-- __init__.py
  |   |-- configure.zcml
  |   |-- models.py
  |   |-- run.py
  |   |-- templates
  |   |   |-- mytemplate.pt
  |   |   `-- static/
  |   |-- tests.py
  |   `-- views.py
  |-- MyProject.ini
  `-- setup.py

The ``MyProject`` :term:`Project`
---------------------------------

The ``MyProject`` :term:`project` is the distribution and deployment
wrapper for your application.  It contains both the ``myproject``
:term:`package` representing your application as well as files used to
describe, run, and test your application.

#. ``CHANGES.txt`` describes the changes you've made to the
   application.  It is conventionally written in
   :term:`ReStructuredText` format.

#. ``README.txt`` describes the application in general.  It is
   conventionally written in :term:`ReStructuredText` format.

#. ``MyProject.ini`` is a :term:`PasteDeploy` configuration file that
   can be used to execute your application.

#. ``setup.py`` is the file you'll use to test and distribute your
   application.  It is a standard :term:`setuptools` ``setup.py``
   file.

.. index::
   single: PasteDeploy
   single: ini file

.. _MyProject_ini:

``MyProject.ini``
~~~~~~~~~~~~~~~~~

The ``MyProject.ini`` file is a :term:`PasteDeploy` configuration
file.  Its purpose is to specify an application to run when you invoke
``paster serve``, as well as the deployment settings provided to that
application.

The generated ``MyProject.ini`` file looks like so:

.. literalinclude:: MyProject/MyProject.ini
   :linenos:

This file contains several "sections" including ``[DEFAULT]``,
``[app:main]``, and ``[server:main]``.

The ``[DEFAULT]`` section consists of global parameters that are
shared by all the applications, servers and :term:`middleware` defined
within the configuration file.  By default it contains one key
``debug``, which is set to ``true``.  This key is used by various
components to decide whether to act in a "debugging" mode.
``repoze.bfg`` itself does not do anything at all with this parameter,
and neither does any template-generated application.

The ``[app:main]`` section represents configuration for your
application.  This section name represents the ``main`` application
(and it's an ``app`` -lication, thus ``app:main``), signifying that
this is the default application run by ``paster serve`` when it is
invoked against this configuration file.  The name ``main`` is a
convention signifying that it the default application.

The ``use`` setting is required in the ``[app:main]`` section.  The
``use`` setting points at a :term:`setuptools` :term:`entry point`
named ``MyProject#app`` (the ``egg:`` prefix in ``egg:MyProject#app``
indicates that this is an entry point *URI* specifier, where the
"scheme" is "egg").

.. sidebar::  ``setuptools`` Entry Points and PasteDeploy ``.ini`` Files

   This part of configuration can be confusing so let's try to clear
   things up a bit.  Take a look at the generated ``setup.py`` file
   for this project.  Note that the ``entry_point`` line in
   ``setup.py`` points at 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 ``app`` (the entry point name) which has a value
   ``myproject.run:app``.  The *key* ``app`` is what our
   ``egg:MyProject#app`` value of the ``use`` section in our config
   file is pointing at.  The value represents a :term:`dotted Python
   name` path, which refers to a callable in our ``myproject``
   package's ``run.py`` module.  In English, this entry point can thus
   be referred to as a "Paste application factory in the ``MyProject``
   project which has the entry point named ``app`` where the entry
   point refers to a ``app`` function in the ``mypackage.run``
   module".  If indeed if you open up the ``run.py`` module generated
   within the ``myproject`` package, you'll see a ``app`` function.
   This is the function called :term:`PasteDeploy` when the ``paster
   serve`` command is invoked against our application.  It accepts a
   global configuration object and *returns* an instance of our
   application.

The ``use`` setting is the only setting required in the ``[app:main]``
section unless you've changed the callable referred to by the
``MyProject#app`` entry point to accept more arguments: other settings
you add to this section are passed as keywords arguments to the
callable represented by this entry point (``app`` in our ``run.py``
module).  You can provide startup-time configuration parameters to
your application by requiring more settings in this section.

The ``reload_templates`` setting in the ``[app:main]`` section is a
:mod:`repoze.bfg` -specific setting which is passed into the
framework.  If it exists, and its value is ``true``, :term:`Chameleon`
template changes will not require an application restart to be
detected.  See :ref:`reload_templates_section` for more information.

.. warning:: The ``reload_templates`` option should be turned off for
   production applications, as template rendering is slowed when it is
   turned on.

Various other settings may exist in this section having to do with
debugging or influencing runtime behavior of a :mod:`repoze.bfg`
application.  See :ref:`environment_chapter` for more information
about these settings.

The ``[server:main]`` section of the configuration file configures a
WSGI server which listens on TCP port 6543.  It is configured to
listen on all interfaces (``0.0.0.0``).  The ``Paste#http`` server
will create a new thread for each request.

.. note::

  In general, :mod:`repoze.bfg` applications generated from ``paster
  templates`` should be threading-aware.  It is not required that a
  :mod:`repoze.bfg` application be nonblocking as all application code
  will run in its own thread, provided by the server you're using.

See the :term:`PasteDeploy` documentation for more information about
other types of things you can put into this ``.ini`` file, such as
other applications, :term:`middleware` and alternate :term:`WSGI`
server implementations.

.. index::
   single: setup.py

``setup.py``
~~~~~~~~~~~~

The ``setup.py`` file is a :term:`setuptools` setup file.  It is meant
to be run directly from the command line to perform a variety of
functions, such as testing your application, packaging, and
distributing your application.

.. note::

  ``setup.py`` is the defacto standard which Python developers use to
  distribute their reusable code.  You can read more about
  ``setup.py`` files and their usage in the `Setuptools documentation
  <http://peak.telecommunity.com/DevCenter/setuptools>`_.

Our generated ``setup.py`` looks like this:

.. literalinclude:: MyProject/setup.py
   :linenos:

The ``setup.py`` file calls the setuptools ``setup`` function, which
does various things depending on the arguments passed to ``setup.py``
on the command line.

Within the arguments to this function call, information about your
application is kept.  While it's beyond the scope of this
documentation to explain everything about setuptools setup files, we'll
provide a whirlwind tour of what exists in this file in this section.

Your application's name can be any string; it is specified in the
``name`` field.  The version number is specified in the ``version``
value.  A short description is provided in the ``description`` field.
The ``long_description`` is conventionally the content of the README
and CHANGES file appended together.  The ``classifiers`` field is a
list of `Trove
<http://pypi.python.org/pypi?%3Aaction=list_classifiers>`_ classifiers
describing your application.  ``author`` and ``author_email`` are text
fields which probably don't need any description.  ``url`` is a field
that should point at your application project's URL (if any).
``packages=find_packages()`` causes all packages within the project to
be found when packaging the application.  ``include_package_data``
will include non-Python files when the application is packaged if
those files are checked into version control.  ``zip_safe`` indicates
that this package is not safe to use as a zipped egg; instead it will
always unpack as a directory, which is more convenient.
``install_requires`` and ``tests_require`` indicate that this package
depends on the ``repoze.bfg`` package.  ``test_suite`` points at the
package for our application, which means all tests found in the
package will be run when ``setup.py test`` is invoked.  We examined
``entry_points`` in our discussion of the ``MyProject.ini`` file; this
file defines the ``app`` entry point that represents our project's
application.

Usually you only need to think about the contents of the ``setup.py``
file when distributing your application to other people, or when
versioning your application for your own use.  For fun, you can try
this command now:

.. code-block:: python

   $ python setup.py sdist

This will create a tarball of your application in a ``dist``
subdirectory named ``MyProject-0.1.tar.gz``.  You can send this
tarball to other people who want to use your application.

.. warning::

   By default, ``setup.py sdist`` does not place non-Python-source
   files in generated tarballs.  This means, in this case, that the
   ``templates/mytemplate.pt`` file and the files in the
   ``templates/static`` directory are not packaged in the tarball.  To
   allow this to happen, check all the files that you'd like to be
   distributed along with your application's Python files into a
   version control system such as Subversion.  After you do this, when
   you rerun ``setup.py sdist``, all files checked into the version
   control system will be included in the tarball.

.. index::
   single: package

The ``myproject`` :term:`Package`
---------------------------------

The ``myproject`` :term:`package` lives inside the ``MyProject``
:term:`project`.  It contains:

#. An ``__init__.py`` file which signifies that this is a Python
   :term:`package`.  It is conventionally empty, save for a single
   comment at the top.

#. A ``configure.zcml`` is a :term:`ZCML` file which maps view names
   to model types.  Its contents populate the :term:`application
   registry` when loaded.

#. A ``models.py`` module, which contains :term:`model` code.

#. A ``run.py`` module, which contains code that helps users run the
   application.

#. A ``templates`` directory, which contains :term:`Chameleon` (or
   other types of) templates.

#. A ``tests.py`` module, which contains unit test code for the
   application.

#. A ``views.py`` module, which contains view code for the
   application.

These are purely conventions established by the ``paster`` template:
:mod:`repoze.bfg` doesn't insist that you name things in any
particular way.

.. index::
   single: configure.zcml

``configure.zcml``
~~~~~~~~~~~~~~~~~~

The ``configure.zcml`` contains configuration statements that populate
the :term:`application registry`. It looks like so:

.. literalinclude:: MyProject/myproject/configure.zcml
   :linenos:
   :language: xml

#. Line 1 provides the root node and namespaces for the configuration
   language.  ``http://namespaces.repoze.org/bfg`` is the default XML
   namespace.  Add-on packages may require other namespaces.

#. Line 4 initializes :mod:`repoze.bfg` -specific configuration
   directives by including the ``repoze.bfg.includes`` package.  This
   causes all of the ZCML within the ``configure.zcml`` of the
   ``repoze.bfg.includes`` package to be "included" in this
   configuration file's scope.  Effectively this means that we can use
   (for this example) the ``view`` and ``static`` directives which
   follow later in this file.

#. Lines 6-10 register a "default view" (a view that has no ``name``
   attribute).  It is registered so that it will be found when the
   :term:`context` of the request is an instance of the
   :class:`myproject.models.MyModel` class.  The ``view`` attribute
   points at a Python function that does all the work for this view,
   also known as a :term:`view callable`.  Note that the values of
   both the ``context`` attribute and the ``view`` attribute begin
   with a single period.  Names that begin with a period are
   "shortcuts" which point at files relative to the :term:`package` in
   which the ``configure.zcml`` file lives.  In this case, since the
   ``configure.zcml`` file lives within the :mod:`myproject` package,
   the shortcut ``.models.MyModel`` could also be spelled
   ``myproject.models.MyModel`` (forming a full Python dotted-path
   name to the ``MyModel`` class).  Likewise the shortcut
   ``.views.my_view`` could be replaced with
   ``myproject.views.my_view``.

   The view declaration also names a ``renderer``, which in this case
   is a template that will be used to render the result of the view
   callable.  This particular view declaration points at
   ``templates/mytemplate.pt``, which is a *relative* file
   specification; it's relative to the directory in which the
   ``configure.zcml`` file lives.  The template file it points at is a
   :term:`Chameleon` ZPT template file.

#. Lines 12-15 register a static view, which will register a view
   which serves up the files from the ``templates/static`` directory
   relative to the directory in which the ``configure.zcml`` file
   lives.

#. Line 17 ends the ``configure`` root tag.

.. index::
   single: views.py

``views.py``
~~~~~~~~~~~~

Much of the heavy lifting in a :mod:`repoze.bfg` application comes in
the form of *view callables*.  A :term:`view callable` is the main
tool of a :mod:`repoze.bfg` web application developer; it is a bit of
code which accepts a :term:`request` and which returns a
:term:`response`.

.. literalinclude:: MyProject/myproject/views.py
   :linenos:

This bit of code was registered as the view callable within
``configure.zcml``.  ``configure.zcml`` said that the default URL for
instances that are of the class :class:`myproject.models.MyModel`
should run this :func:`myproject.views.my_view` function.

This view callable function is handed a single piece of information:
the :term:`request`.  The *request* is an instance of the
:term:`WebOb` ``Request`` class representing the browser's request to
our server.

This view returns a dictionary.  When this view is invoked, a
:term:`renderer` converts the dictionary returned by the view into
HTML, and returns the result as the :term:`response`.  This view is
configured to invoke a renderer which uses a :term:`Chameleon` ZPT
template (``templates/my_template.pt``, as specified in the
``configure.zcml`` file).

See :ref:`views_which_use_a_renderer` for more information about how
views, renderers, and templates relate and cooperate.

.. note:: because our ``MyProject.ini`` has a ``reload_templates =
   true`` directive indicating that templates should be reloaded when
   they change, you won't need to restart the application server to
   see changes you make to templates.  During development, this is
   handy.  If this directive had been ``false`` (or if the directive
   did not exist), you would need to restart the application server
   for each template change.  For production applications, you should
   set your project's ``reload_templates`` to ``false`` to increase
   the speed at which templates may be rendered.

.. index::
   single: models.py

.. _modelspy_project_section:

``models.py``
~~~~~~~~~~~~~

The ``models.py`` module provides the :term:`model` data and behavior
for our application.  Models are objects which store application data
and provide APIs which mutate and return this data.  We write a class
named ``MyModel`` that provides the behavior.

.. literalinclude:: MyProject/myproject/models.py
   :linenos:

#. Lines 1-2 define the MyModel class.

#. Line 4 defines an instance of MyModel as the root.

#. Line 6 is a "root factory" function that will be called by the
   :mod:`repoze.bfg` *Router* for each request when it wants to find
   the root of the object graph.  Conventionally this is called
   ``get_root``.

In a "real" application, the root object would not be such a simple
object.  Instead, it would be an object that could access some
persistent data store, such as a database.  :mod:`repoze.bfg` doesn't
make any assumption about which sort of datastore you'll want to use,
so the sample application uses an instance of
:class:`myproject.models.MyModel` to represent the root.

.. index::
   single: run.py

``run.py``
~~~~~~~~~~

We need a small Python module that configures our application and
which advertises an entry point for use by our :term:`PasteDeploy`
``.ini`` file.  This is the file named ``run.py``:

.. literalinclude:: MyProject/myproject/run.py
   :linenos:

#. Line 1 imports the :term:`Configurator` class from
   :mod:`repoze.bfg.configuration` that we use later.

#. Line 2 imports the ``get_root`` function from
   :mod:`myproject.models` that we use later.

#. Lines 4-13 define a function that returns a :mod:`repoze.bfg`
   WSGI application.  This function is meant to be called
   by the :term:`PasteDeploy` framework as a result of running
   ``paster serve``.

``templates/mytemplate.pt``
~~~~~~~~~~~~~~~~~~~~~~~~~~~

The single :term:`Chameleon` template exists in the project.  Its
contents are too long to show here, but it displays a default page
when rendered.  It is referenced by the ``view`` declaration's
``renderer`` attribute in the ``configure.zcml`` file.  See
:ref:`views_which_use_a_renderer` for more information about
renderers.

Templates are accessed and used by view configurations and sometimes
by view functions themselves.  See :ref:`templates_used_directly` and
:ref:`templates_used_as_renderers`.

``templates/static``
~~~~~~~~~~~~~~~~~~~~

This directory contains static resources which support the
``mytemplate.pt`` template.  It includes CSS and images.

.. index::
   single: tests.py

``tests.py``
~~~~~~~~~~~~

The ``tests.py`` module includes unit tests for your application.

.. literalinclude:: MyProject/myproject/tests.py
   :linenos:

This sample ``tests.py`` file has a single unit test defined within
it.  This test is executed when you run ``python setup.py test``.  You
may add more tests here as you build your application.  You are not
required to write tests to use :mod:`repoze.bfg`, this file is simply
provided as convenience and example.

See :ref:`unittesting_chapter` for more information about writing
:mod:`repoze.bfg` unit tests.