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============================================
02: Python Packages for Pyramid Applications
============================================
Most modern Python development is done using Python packages, an approach
Pyramid puts to good use. In this step we redo "Hello World" as a
minimum Python package inside a minimum Python project.
Background
==========
Python developers can organize a collection of modules and files into a
namespaced unit called a :ref:`package <python:tut-packages>`. If a
directory is on ``sys.path`` and has a special file named
``__init__.py``, it is treated as a Python package.
Packages can be bundled up, made available for installation,
and installed through a (muddled, but improving) toolchain oriented
around a ``setup.py`` file for a
`setuptools project <http://pythonhosted.org/setuptools/setuptools.html>`_.
Explaining it all in this
tutorial will induce madness. For this tutorial, this is all you need to
know:
- We will have a directory for each tutorial step as a setuptools *project*
- This project will contain a ``setup.py`` which injects the features
of the setuptool's project machinery into the directory
- In this project we will make a ``tutorial`` subdirectory into a Python
*package* using an ``__init__.py`` Python module file
- We will run ``python setup.py develop`` to install our project in
development mode
In summary:
- You'll do your development in a Python *package*
- That package will be part of a setuptools *project*
Objectives
==========
- Make a Python "package" directory with an ``__init__.py``
- Get a minimum Python "project" in place by making a ``setup.py``
- Install our ``tutorial`` project in development mode
Steps
=====
#. Make an area for this tutorial step:
.. code-block:: bash
$ cd ..; mkdir package; cd package
#. In ``package/setup.py``, enter the following:
.. literalinclude:: package/setup.py
#. Make the new project installed for development then make a directory
for the actual code:
.. code-block:: bash
$ $VENV/bin/python setup.py develop
$ mkdir tutorial
#. Enter the following into ``package/tutorial/__init__.py``:
.. literalinclude:: package/tutorial/__init__.py
#. Enter the following into ``package/tutorial/app.py``:
.. literalinclude:: package/tutorial/app.py
#. Run the WSGI application with:
.. code-block:: bash
$ $VENV/bin/python tutorial/app.py
#. Open http://localhost:6543/ in your browser.
Analysis
========
Python packages give us an organized unit of project development.
Python projects, via ``setup.py``, gives us special features when
our package is installed (in this case, in local development mode.)
In this step we have a Python package called ``tutorial``. We use the
same name in each step of the tutorial, to avoid unnecessary retyping.
Above this ``tutorial`` directory we have the files that handle the
packaging of this project. At the moment, all we need is a
bare-bones ``setup.py``.
Everything else is the same about our application. We simply made a
Python package with a ``setup.py`` and installed it in development mode.
Note that the way we're running the app (``python tutorial/app.py``) is a bit
of an odd duck. We would never do this unless we were writing a tutorial that
tries to capture how this stuff works a step at a time. It's generally a bad
idea to run a Python module inside a package directly as a script.
.. seealso:: :ref:`Python Packages <python:tut-packages>`,
`setuptools Entry Points <http://pythonhosted.org/setuptools/pkg_resources.html#entry-points>`_
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