2. Writing the Setup Script
***************************

The setup script is the centre of all activity in building,
distributing, and installing modules using the Distutils.  The main
purpose of the setup script is to describe your module distribution to
the Distutils, so that the various commands that operate on your
modules do the right thing.  As we saw in section A Simple Example
above, the setup script consists mainly of a call to "setup()", and
most information supplied to the Distutils by the module developer is
supplied as keyword arguments to "setup()".

Here’s a slightly more involved example, which we’ll follow for the
next couple of sections: the Distutils’ own setup script.  (Keep in
mind that although the Distutils are included with Python 1.6 and
later, they also have an independent existence so that Python 1.5.2
users can use them to install other module distributions.  The
Distutils’ own setup script, shown here, is used to install the
package into Python 1.5.2.)

   #!/usr/bin/env python

   from distutils.core import setup

   setup(name='Distutils',
         version='1.0',
         description='Python Distribution Utilities',
         author='Greg Ward',
         author_email='gward@python.net',
         url='https://www.python.org/sigs/distutils-sig/',
         packages=['distutils', 'distutils.command'],
        )

There are only two differences between this and the trivial one-file
distribution presented in section A Simple Example: more metadata, and
the specification of pure Python modules by package, rather than by
module.  This is important since the Distutils consist of a couple of
dozen modules split into (so far) two packages; an explicit list of
every module would be tedious to generate and difficult to maintain.
For more information on the additional meta-data, see section
Additional meta-data.

Note that any pathnames (files or directories) supplied in the setup
script should be written using the Unix convention, i.e. slash-
separated.  The Distutils will take care of converting this platform-
neutral representation into whatever is appropriate on your current
platform before actually using the pathname.  This makes your setup
script portable across operating systems, which of course is one of
the major goals of the Distutils.  In this spirit, all pathnames in
this document are slash-separated.

This, of course, only applies to pathnames given to Distutils
functions.  If you, for example, use standard Python functions such as
"glob.glob()" or "os.listdir()" to specify files, you should be
careful to write portable code instead of hardcoding path separators:

   glob.glob(os.path.join('mydir', 'subdir', '*.html'))
   os.listdir(os.path.join('mydir', 'subdir'))


2.1. Listing whole packages
===========================

The "packages" option tells the Distutils to process (build,
distribute, install, etc.) all pure Python modules found in each
package mentioned in the "packages" list.  In order to do this, of
course, there has to be a correspondence between package names and
directories in the filesystem.  The default correspondence is the most
obvious one, i.e. package "distutils" is found in the directory
"distutils" relative to the distribution root. Thus, when you say
"packages = ['foo']" in your setup script, you are promising that the
Distutils will find a file "foo/__init__.py" (which might be spelled
differently on your system, but you get the idea) relative to the
directory where your setup script lives.  If you break this promise,
the Distutils will issue a warning but still process the broken
package anyway.

If you use a different convention to lay out your source directory,
that’s no problem: you just have to supply the "package_dir" option to
tell the Distutils about your convention.  For example, say you keep
all Python source under "lib", so that modules in the “root package”
(i.e., not in any package at all) are in "lib", modules in the "foo"
package are in "lib/foo", and so forth.  Then you would put

   package_dir = {'': 'lib'}

in your setup script.  The keys to this dictionary are package names,
and an empty package name stands for the root package.  The values are
directory names relative to your distribution root.  In this case,
when you say "packages = ['foo']", you are promising that the file
"lib/foo/__init__.py" exists.

Another possible convention is to put the "foo" package right in
"lib", the "foo.bar" package in "lib/bar", etc.  This would be written
in the setup script as

   package_dir = {'foo': 'lib'}

A "package: dir" entry in the "package_dir" dictionary implicitly
applies to all packages below *package*, so the "foo.bar" case is
automatically handled here.  In this example, having "packages =
['foo', 'foo.bar']" tells the Distutils to look for "lib/__init__.py"
and "lib/bar/__init__.py".  (Keep in mind that although "package_dir"
applies recursively, you must explicitly list all packages in
"packages": the Distutils will *not* recursively scan your source tree
looking for any directory with an "__init__.py" file.)


2.2. Listing individual modules
===============================

For a small module distribution, you might prefer to list all modules
rather than listing packages—especially the case of a single module
that goes in the “root package” (i.e., no package at all).  This
simplest case was shown in section A Simple Example; here is a
slightly more involved example:

   py_modules = ['mod1', 'pkg.mod2']

This describes two modules, one of them in the “root” package, the
other in the "pkg" package.  Again, the default package/directory
layout implies that these two modules can be found in "mod1.py" and
"pkg/mod2.py", and that "pkg/__init__.py" exists as well. And again,
you can override the package/directory correspondence using the
"package_dir" option.


2.3. Describing extension modules
=================================

Just as writing Python extension modules is a bit more complicated
than writing pure Python modules, describing them to the Distutils is
a bit more complicated. Unlike pure modules, it’s not enough just to
list modules or packages and expect the Distutils to go out and find
the right files; you have to specify the extension name, source
file(s), and any compile/link requirements (include directories,
libraries to link with, etc.).

All of this is done through another keyword argument to "setup()", the
"ext_modules" option.  "ext_modules" is just a list of "Extension"
instances, each of which describes a single extension module. Suppose
your distribution includes a single extension, called "foo" and
implemented by "foo.c".  If no additional instructions to the
compiler/linker are needed, describing this extension is quite simple:

   Extension('foo', ['foo.c'])

The "Extension" class can be imported from "distutils.core" along with
"setup()".  Thus, the setup script for a module distribution that
contains only this one extension and nothing else might be:

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

The "Extension" class (actually, the underlying extension-building
machinery implemented by the **build_ext** command) supports a great
deal of flexibility in describing Python extensions, which is
explained in the following sections.


2.3.1. Extension names and packages
-----------------------------------

The first argument to the "Extension" constructor is always the name
of the extension, including any package names.  For example,

   Extension('foo', ['src/foo1.c', 'src/foo2.c'])

describes an extension that lives in the root package, while

   Extension('pkg.foo', ['src/foo1.c', 'src/foo2.c'])

describes the same extension in the "pkg" package.  The source files
and resulting object code are identical in both cases; the only
difference is where in the filesystem (and therefore where in Python’s
namespace hierarchy) the resulting extension lives.

If you have a number of extensions all in the same package (or all
under the same base package), use the "ext_package" keyword argument
to "setup()".  For example,

   setup(...,
         ext_package='pkg',
         ext_modules=[Extension('foo', ['foo.c']),
                      Extension('subpkg.bar', ['bar.c'])],
        )

will compile "foo.c" to the extension "pkg.foo", and "bar.c" to
"pkg.subpkg.bar".


2.3.2. Extension source files
-----------------------------

The second argument to the "Extension" constructor is a list of source
files.  Since the Distutils currently only support C, C++, and
Objective-C extensions, these are normally C/C++/Objective-C source
files.  (Be sure to use appropriate extensions to distinguish C++
source files: ".cc" and ".cpp" seem to be recognized by both Unix and
Windows compilers.)

However, you can also include SWIG interface (".i") files in the list;
the **build_ext** command knows how to deal with SWIG extensions: it
will run SWIG on the interface file and compile the resulting C/C++
file into your extension.

This warning notwithstanding, options to SWIG can be currently passed
like this:

   setup(...,
         ext_modules=[Extension('_foo', ['foo.i'],
                                swig_opts=['-modern', '-I../include'])],
         py_modules=['foo'],
        )

Or on the commandline like this:

   > python setup.py build_ext --swig-opts="-modern -I../include"

On some platforms, you can include non-source files that are processed
by the compiler and included in your extension.  Currently, this just
means Windows message text (".mc") files and resource definition
(".rc") files for Visual C++. These will be compiled to binary
resource (".res") files and linked into the executable.


2.3.3. Preprocessor options
---------------------------

Three optional arguments to "Extension" will help if you need to
specify include directories to search or preprocessor macros to
define/undefine: "include_dirs", "define_macros", and "undef_macros".

For example, if your extension requires header files in the "include"
directory under your distribution root, use the "include_dirs" option:

   Extension('foo', ['foo.c'], include_dirs=['include'])

You can specify absolute directories there; if you know that your
extension will only be built on Unix systems with X11R6 installed to
"/usr", you can get away with

   Extension('foo', ['foo.c'], include_dirs=['/usr/include/X11'])

You should avoid this sort of non-portable usage if you plan to
distribute your code: it’s probably better to write C code like

   #include <X11/Xlib.h>

If you need to include header files from some other Python extension,
you can take advantage of the fact that header files are installed in
a consistent way by the Distutils **install_headers** command.  For
example, the Numerical Python header files are installed (on a
standard Unix installation) to
"/usr/local/include/python1.5/Numerical". (The exact location will
differ according to your platform and Python installation.)  Since the
Python include directory—"/usr/local/include/python1.5" in this
case—is always included in the search path when building Python
extensions, the best approach is to write C code like

   #include <Numerical/arrayobject.h>

If you must put the "Numerical" include directory right into your
header search path, though, you can find that directory using the
Distutils "distutils.sysconfig" module:

   from distutils.sysconfig import get_python_inc
   incdir = os.path.join(get_python_inc(plat_specific=1), 'Numerical')
   setup(...,
         Extension(..., include_dirs=[incdir]),
         )

Even though this is quite portable—it will work on any Python
installation, regardless of platform—it’s probably easier to just
write your C code in the sensible way.

You can define and undefine pre-processor macros with the
"define_macros" and "undef_macros" options. "define_macros" takes a
list of "(name, value)" tuples, where "name" is the name of the macro
to define (a string) and "value" is its value: either a string or
"None".  (Defining a macro "FOO" to "None" is the equivalent of a bare
"#define FOO" in your C source: with most compilers, this sets "FOO"
to the string "1".)  "undef_macros" is just a list of macros to
undefine.

For example:

   Extension(...,
             define_macros=[('NDEBUG', '1'),
                            ('HAVE_STRFTIME', None)],
             undef_macros=['HAVE_FOO', 'HAVE_BAR'])

is the equivalent of having this at the top of every C source file:

   #define NDEBUG 1
   #define HAVE_STRFTIME
   #undef HAVE_FOO
   #undef HAVE_BAR


2.3.4. Library options
----------------------

You can also specify the libraries to link against when building your
extension, and the directories to search for those libraries.  The
"libraries" option is a list of libraries to link against,
"library_dirs" is a list of directories to search for libraries at
link-time, and "runtime_library_dirs" is a list of directories to
search for shared (dynamically loaded) libraries at run-time.

For example, if you need to link against libraries known to be in the
standard library search path on target systems

   Extension(...,
             libraries=['gdbm', 'readline'])

If you need to link with libraries in a non-standard location, you’ll
have to include the location in "library_dirs":

   Extension(...,
             library_dirs=['/usr/X11R6/lib'],
             libraries=['X11', 'Xt'])

(Again, this sort of non-portable construct should be avoided if you
intend to distribute your code.)


2.3.5. Other options
--------------------

There are still some other options which can be used to handle special
cases.

The "optional" option is a boolean; if it is true, a build failure in
the extension will not abort the build process, but instead simply not
install the failing extension.

The "extra_objects" option is a list of object files to be passed to
the linker. These files must not have extensions, as the default
extension for the compiler is used.

"extra_compile_args" and "extra_link_args" can be used to specify
additional command line options for the respective compiler and linker
command lines.

"export_symbols" is only useful on Windows.  It can contain a list of
symbols (functions or variables) to be exported. This option is not
needed when building compiled extensions: Distutils  will
automatically add "initmodule" to the list of exported symbols.

The "depends" option is a list of files that the extension depends on
(for example header files). The build command will call the compiler
on the sources to rebuild extension if any on this files has been
modified since the previous build.


2.4. Relationships between Distributions and Packages
=====================================================

A distribution may relate to packages in three specific ways:

1. It can require packages or modules.

2. It can provide packages or modules.

3. It can obsolete packages or modules.

These relationships can be specified using keyword arguments to the
"distutils.core.setup()" function.

Dependencies on other Python modules and packages can be specified by
supplying the *requires* keyword argument to "setup()". The value must
be a list of strings.  Each string specifies a package that is
required, and optionally what versions are sufficient.

To specify that any version of a module or package is required, the
string should consist entirely of the module or package name. Examples
include "'mymodule'" and "'xml.parsers.expat'".

If specific versions are required, a sequence of qualifiers can be
supplied in parentheses.  Each qualifier may consist of a comparison
operator and a version number.  The accepted comparison operators are:

   <    >    ==
   <=   >=   !=

These can be combined by using multiple qualifiers separated by commas
(and optional whitespace).  In this case, all of the qualifiers must
be matched; a logical AND is used to combine the evaluations.

Let’s look at a bunch of examples:

+---------------------------+------------------------------------------------+
| Requires Expression       | Explanation                                    |
+===========================+================================================+
| "==1.0"                   | Only version "1.0" is compatible               |
+---------------------------+------------------------------------------------+
| ">1.0, !=1.5.1, <2.0"     | Any version after "1.0" and before "2.0" is    |
|                           | compatible, except "1.5.1"                     |
+---------------------------+------------------------------------------------+

Now that we can specify dependencies, we also need to be able to
specify what we provide that other distributions can require.  This is
done using the *provides* keyword argument to "setup()". The value for
this keyword is a list of strings, each of which names a Python module
or package, and optionally identifies the version.  If the version is
not specified, it is assumed to match that of the distribution.

Some examples:

+-----------------------+------------------------------------------------+
| Provides Expression   | Explanation                                    |
+=======================+================================================+
| "mypkg"               | Provide "mypkg", using the distribution        |
|                       | version                                        |
+-----------------------+------------------------------------------------+
| "mypkg (1.1)"         | Provide "mypkg" version 1.1, regardless of the |
|                       | distribution version                           |
+-----------------------+------------------------------------------------+

A package can declare that it obsoletes other packages using the
*obsoletes* keyword argument.  The value for this is similar to that
of the *requires* keyword: a list of strings giving module or package
specifiers.  Each specifier consists of a module or package name
optionally followed by one or more version qualifiers.  Version
qualifiers are given in parentheses after the module or package name.

The versions identified by the qualifiers are those that are obsoleted
by the distribution being described.  If no qualifiers are given, all
versions of the named module or package are understood to be
obsoleted.


2.5. Installing Scripts
=======================

So far we have been dealing with pure and non-pure Python modules,
which are usually not run by themselves but imported by scripts.

Scripts are files containing Python source code, intended to be
started from the command line.  Scripts don’t require Distutils to do
anything very complicated. The only clever feature is that if the
first line of the script starts with "#!" and contains the word
“python”, the Distutils will adjust the first line to refer to the
current interpreter location. By default, it is replaced with the
current interpreter location.  The "--executable" (or "-e") option
will allow the interpreter path to be explicitly overridden.

The "scripts" option simply is a list of files to be handled in this
way.  From the PyXML setup script:

   setup(...,
         scripts=['scripts/xmlproc_parse', 'scripts/xmlproc_val']
         )

Changed in version 3.1: All the scripts will also be added to the
"MANIFEST" file if no template is provided.  See Specifying the files
to distribute.


2.6. Installing Package Data
============================

Often, additional files need to be installed into a package.  These
files are often data that’s closely related to the package’s
implementation, or text files containing documentation that might be
of interest to programmers using the package.  These files are called
*package data*.

Package data can be added to packages using the "package_data" keyword
argument to the "setup()" function.  The value must be a mapping from
package name to a list of relative path names that should be copied
into the package.  The paths are interpreted as relative to the
directory containing the package (information from the "package_dir"
mapping is used if appropriate); that is, the files are expected to be
part of the package in the source directories. They may contain glob
patterns as well.

The path names may contain directory portions; any necessary
directories will be created in the installation.

For example, if a package should contain a subdirectory with several
data files, the files can be arranged like this in the source tree:

   setup.py
   src/
       mypkg/
           __init__.py
           module.py
           data/
               tables.dat
               spoons.dat
               forks.dat

The corresponding call to "setup()" might be:

   setup(...,
         packages=['mypkg'],
         package_dir={'mypkg': 'src/mypkg'},
         package_data={'mypkg': ['data/*.dat']},
         )

Changed in version 3.1: All the files that match "package_data" will
be added to the "MANIFEST" file if no template is provided.  See
Specifying the files to distribute.


2.7. Installing Additional Files
================================

The "data_files" option can be used to specify additional files needed
by the module distribution: configuration files, message catalogs,
data files, anything which doesn’t fit in the previous categories.

"data_files" specifies a sequence of (*directory*, *files*) pairs in
the following way:

   setup(...,
         data_files=[('bitmaps', ['bm/b1.gif', 'bm/b2.gif']),
                     ('config', ['cfg/data.cfg']),
                     ('/etc/init.d', ['init-script'])]
        )

Note that you can specify the directory names where the data files
will be installed, but you cannot rename the data files themselves.

Each (*directory*, *files*) pair in the sequence specifies the
installation directory and the files to install there.  If *directory*
is a relative path, it is interpreted relative to the installation
prefix (Python’s "sys.prefix" for pure-Python packages,
"sys.exec_prefix" for packages that contain extension modules).  Each
file name in *files* is interpreted relative to the "setup.py" script
at the top of the package source distribution.  No directory
information from *files* is used to determine the final location of
the installed file; only the name of the file is used.

You can specify the "data_files" options as a simple sequence of files
without specifying a target directory, but this is not recommended,
and the **install** command will print a warning in this case. To
install data files directly in the target directory, an empty string
should be given as the directory.

Changed in version 3.1: All the files that match "data_files" will be
added to the "MANIFEST" file if no template is provided.  See
Specifying the files to distribute.


2.8. Additional meta-data
=========================

The setup script may include additional meta-data beyond the name and
version. This information includes:

+------------------------+-----------------------------+-------------------+----------+
| Meta-Data              | Description                 | Value             | Notes    |
+========================+=============================+===================+==========+
| "name"                 | name of the package         | short string      | (1)      |
+------------------------+-----------------------------+-------------------+----------+
| "version"              | version of this release     | short string      | (1)(2)   |
+------------------------+-----------------------------+-------------------+----------+
| "author"               | package author’s name       | short string      | (3)      |
+------------------------+-----------------------------+-------------------+----------+
| "author_email"         | email address of the        | email address     | (3)      |
|                        | package author              |                   |          |
+------------------------+-----------------------------+-------------------+----------+
| "maintainer"           | package maintainer’s name   | short string      | (3)      |
+------------------------+-----------------------------+-------------------+----------+
| "maintainer_email"     | email address of the        | email address     | (3)      |
|                        | package maintainer          |                   |          |
+------------------------+-----------------------------+-------------------+----------+
| "url"                  | home page for the package   | URL               | (1)      |
+------------------------+-----------------------------+-------------------+----------+
| "description"          | short, summary description  | short string      |          |
|                        | of the package              |                   |          |
+------------------------+-----------------------------+-------------------+----------+
| "long_description"     | longer description of the   | long string       | (5)      |
|                        | package                     |                   |          |
+------------------------+-----------------------------+-------------------+----------+
| "download_url"         | location where the package  | URL               | (4)      |
|                        | may be downloaded           |                   |          |
+------------------------+-----------------------------+-------------------+----------+
| "classifiers"          | a list of classifiers       | list of strings   | (4)      |
+------------------------+-----------------------------+-------------------+----------+
| "platforms"            | a list of platforms         | list of strings   |          |
+------------------------+-----------------------------+-------------------+----------+
| "license"              | license for the package     | short string      | (6)      |
+------------------------+-----------------------------+-------------------+----------+

Notes:

1. These fields are required.

2. It is recommended that versions take the form
   *major.minor[.patch[.sub]]*.

3. Either the author or the maintainer must be identified. If
   maintainer is provided, distutils lists it as the author in "PKG-
   INFO".

4. These fields should not be used if your package is to be
   compatible with Python versions prior to 2.2.3 or 2.3.  The list is
   available from the PyPI website.

5. The "long_description" field is used by PyPI when you are
   registering a package, to build its home page.

6. The "license" field is a text indicating the license covering
   the package where the license is not a selection from the “License”
   Trove classifiers. See the "Classifier" field. Notice that there’s
   a "licence" distribution option which is deprecated but still acts
   as an alias for "license".

‘short string’
   A single line of text, not more than 200 characters.

‘long string’
   Multiple lines of plain text in reStructuredText format (see
   http://docutils.sourceforge.net/).

‘list of strings’
   See below.

Encoding the version information is an art in itself. Python packages
generally adhere to the version format *major.minor[.patch][sub]*. The
major number is 0 for initial, experimental releases of software. It
is incremented for releases that represent major milestones in a
package. The minor number is incremented when important new features
are added to the package. The patch number increments when bug-fix
releases are made. Additional trailing version information is
sometimes used to indicate sub-releases.  These are “a1,a2,…,aN” (for
alpha releases, where functionality and API may change), “b1,b2,…,bN”
(for beta releases, which only fix bugs) and “pr1,pr2,…,prN” (for
final pre-release release testing). Some examples:

0.1.0
   the first, experimental release of a package

1.0.1a2
   the second alpha release of the first patch version of 1.0

"classifiers" are specified in a Python list:

   setup(...,
         classifiers=[
             'Development Status :: 4 - Beta',
             'Environment :: Console',
             'Environment :: Web Environment',
             'Intended Audience :: End Users/Desktop',
             'Intended Audience :: Developers',
             'Intended Audience :: System Administrators',
             'License :: OSI Approved :: Python Software Foundation License',
             'Operating System :: MacOS :: MacOS X',
             'Operating System :: Microsoft :: Windows',
             'Operating System :: POSIX',
             'Programming Language :: Python',
             'Topic :: Communications :: Email',
             'Topic :: Office/Business',
             'Topic :: Software Development :: Bug Tracking',
             ],
         )


2.9. Debugging the setup script
===============================

Sometimes things go wrong, and the setup script doesn’t do what the
developer wants.

Distutils catches any exceptions when running the setup script, and
print a simple error message before the script is terminated.  The
motivation for this behaviour is to not confuse administrators who
don’t know much about Python and are trying to install a package.  If
they get a big long traceback from deep inside the guts of Distutils,
they may think the package or the Python installation is broken
because they don’t read all the way down to the bottom and see that
it’s a permission problem.

On the other hand, this doesn’t help the developer to find the cause
of the failure. For this purpose, the "DISTUTILS_DEBUG" environment
variable can be set to anything except an empty string, and distutils
will now print detailed information about what it is doing, dump the
full traceback when an exception occurs, and print the whole command
line when an external program (like a C compiler) fails.
