
An Introduction to Distutils
****************************

This document covers using the Distutils to distribute your Python
modules, concentrating on the role of developer/distributor: if you're
looking for information on installing Python modules, you should refer
to the *Installing Python Modules (Legacy version)* chapter.


Concepts & Terminology
======================

Using the Distutils is quite simple, both for module developers and
for users/administrators installing third-party modules.  As a
developer, your responsibilities (apart from writing solid, well-
documented and well-tested code, of course!) are:

* write a setup script ("setup.py" by convention)

* (optional) write a setup configuration file

* create a source distribution

* (optional) create one or more built (binary) distributions

Each of these tasks is covered in this document.

Not all module developers have access to a multitude of platforms, so
it's not always feasible to expect them to create a multitude of built
distributions.  It is hoped that a class of intermediaries, called
*packagers*, will arise to address this need.  Packagers will take
source distributions released by module developers, build them on one
or more platforms, and release the resulting built distributions.
Thus, users on the most popular platforms will be able to install most
popular Python module distributions in the most natural way for their
platform, without having to run a single setup script or compile a
line of code.


A Simple Example
================

The setup script is usually quite simple, although since it's written
in Python, there are no arbitrary limits to what you can do with it,
though you should be careful about putting arbitrarily expensive
operations in your setup script. Unlike, say, Autoconf-style configure
scripts, the setup script may be run multiple times in the course of
building and installing your module distribution.

If all you want to do is distribute a module called "foo", contained
in a file "foo.py", then your setup script can be as simple as this:

   from distutils.core import setup
   setup(name='foo',
         version='1.0',
         py_modules=['foo'],
         )

Some observations:

* most information that you supply to the Distutils is supplied as
  keyword arguments to the "setup()" function

* those keyword arguments fall into two categories: package metadata
  (name, version number) and information about what's in the package
  (a list of pure Python modules, in this case)

* modules are specified by module name, not filename (the same will
  hold true for packages and extensions)

* it's recommended that you supply a little more metadata, in
  particular your name, email address and a URL for the project (see
  section *Writing the Setup Script* for an example)

To create a source distribution for this module, you would create a
setup script, "setup.py", containing the above code, and run this
command from a terminal:

   python setup.py sdist

For Windows, open a command prompt window (*Start ‣ Accessories*) and
change the command to:

   setup.py sdist

**sdist** will create an archive file (e.g., tarball on Unix, ZIP file
on Windows) containing your setup script "setup.py", and your module
"foo.py". The archive file will be named "foo-1.0.tar.gz" (or ".zip"),
and will unpack into a directory "foo-1.0".

If an end-user wishes to install your "foo" module, all she has to do
is download "foo-1.0.tar.gz" (or ".zip"), unpack it, and---from the
"foo-1.0" directory---run

   python setup.py install

which will ultimately copy "foo.py" to the appropriate directory for
third-party modules in their Python installation.

This simple example demonstrates some fundamental concepts of the
Distutils. First, both developers and installers have the same basic
user interface, i.e. the setup script.  The difference is which
Distutils *commands* they use: the **sdist** command is almost
exclusively for module developers, while **install** is more often for
installers (although most developers will want to install their own
code occasionally).

If you want to make things really easy for your users, you can create
one or more built distributions for them.  For instance, if you are
running on a Windows machine, and want to make things easy for other
Windows users, you can create an executable installer (the most
appropriate type of built distribution for this platform) with the
**bdist_wininst** command.  For example:

   python setup.py bdist_wininst

will create an executable installer, "foo-1.0.win32.exe", in the
current directory.

Other useful built distribution formats are RPM, implemented by the
**bdist_rpm** command, Solaris **pkgtool** (**bdist_pkgtool**), and
HP-UX **swinstall** (**bdist_sdux**).  For example, the following
command will create an RPM file called "foo-1.0.noarch.rpm":

   python setup.py bdist_rpm

(The **bdist_rpm** command uses the **rpm** executable, therefore this
has to be run on an RPM-based system such as Red Hat Linux, SuSE
Linux, or Mandrake Linux.)

You can find out what distribution formats are available at any time
by running

   python setup.py bdist --help-formats


General Python terminology
==========================

If you're reading this document, you probably have a good idea of what
modules, extensions, and so forth are.  Nevertheless, just to be sure
that everyone is operating from a common starting point, we offer the
following glossary of common Python terms:

module
   the basic unit of code reusability in Python: a block of code
   imported by some other code.  Three types of modules concern us
   here: pure Python modules, extension modules, and packages.

pure Python module
   a module written in Python and contained in a single ".py" file
   (and possibly associated ".pyc" and/or ".pyo" files).  Sometimes
   referred to as a "pure module."

extension module
   a module written in the low-level language of the Python
   implementation: C/C++ for Python, Java for Jython. Typically
   contained in a single dynamically loadable pre-compiled file, e.g.
   a shared object (".so") file for Python extensions on Unix, a DLL
   (given the ".pyd" extension) for Python extensions on Windows, or a
   Java class file for Jython extensions.  (Note that currently, the
   Distutils only handles C/C++ extensions for Python.)

package
   a module that contains other modules; typically contained in a
   directory in the filesystem and distinguished from other
   directories by the presence of a file "__init__.py".

root package
   the root of the hierarchy of packages.  (This isn't really a
   package, since it doesn't have an "__init__.py" file.  But we have
   to call it something.) The vast majority of the standard library is
   in the root package, as are many small, standalone third-party
   modules that don't belong to a larger module collection. Unlike
   regular packages, modules in the root package can be found in many
   directories: in fact, every directory listed in "sys.path"
   contributes modules to the root package.


Distutils-specific terminology
==============================

The following terms apply more specifically to the domain of
distributing Python modules using the Distutils:

module distribution
   a collection of Python modules distributed together as a single
   downloadable resource and meant to be installed *en masse*.
   Examples of some well-known module distributions are NumPy, SciPy,
   PIL (the Python Imaging Library), or mxBase.  (This would be called
   a *package*, except that term is already taken in the Python
   context: a single module distribution may contain zero, one, or
   many Python packages.)

pure module distribution
   a module distribution that contains only pure Python modules and
   packages. Sometimes referred to as a "pure distribution."

non-pure module distribution
   a module distribution that contains at least one extension module.
   Sometimes referred to as a "non-pure distribution."

distribution root
   the top-level directory of your source tree (or  source
   distribution); the directory where "setup.py" exists.  Generally
   "setup.py" will be run from this directory.
