6 Creating Built Distributions

A ``built distribution'' is what you're probably used to thinking of either as a ``binary package'' or an ``installer'' (depending on your background). It's not necessarily binary, though, because it might contain only Python source code and/or byte-code; and we don't call it a package, because that word is already spoken for in Python. (And ``installer'' is a term specific to the Windows world. ** do Mac people use it? **)

A built distribution is how you make life as easy as possible for installers of your module distribution: for users of RPM-based Linux systems, it's a binary RPM; for Windows users, it's an executable installer; for Debian-based Linux users, it's a Debian package; and so forth. Obviously, no one person will be able to create built distributions for every platform under the sun, so the Distutils are designed to enable module developers to concentrate on their specialty--writing code and creating source distributions--while an intermediary species called packagers springs up to turn source distributions into built distributions for as many platforms as there are packagers.

Of course, the module developer could be his own packager; or the packager could be a volunteer ``out there'' somewhere who has access to a platform which the original developer does not; or it could be software periodically grabbing new source distributions and turning them into built distributions for as many platforms as the software has access to. Regardless of who they are, a packager uses the setup script and the bdist command family to generate built distributions.

As a simple example, if I run the following command in the Distutils source tree:

python setup.py bdist

then the Distutils builds my module distribution (the Distutils itself in this case), does a ``fake'' installation (also in the build directory), and creates the default type of built distribution for my platform. The default format for built distributions is a ``dumb'' tar file on Unix, and a simple executable installer on Windows. (That tar file is considered ``dumb'' because it has to be unpacked in a specific location to work.)

Thus, the above command on a Unix system creates Distutils-1.0.plat.tar.gz; unpacking this tarball from the right place installs the Distutils just as though you had downloaded the source distribution and run

python setup.py
  install

. (The ``right place'' is either the root of the filesystem or Python's prefix directory, depending on the options given to the bdist_dumb command; the default is to make dumb distributions relative to prefix.)

Obviously, for pure Python distributions, this isn't any simpler than just running python setup.py install--but for non-pure distributions, which include extensions that would need to be compiled, it can mean the difference between someone being able to use your extensions or not. And creating ``smart'' built distributions, such as an RPM package or an executable installer for Windows, is far more convenient for users even if your distribution doesn't include any extensions.

The bdist command has a --formats option, similar to the sdist command, which you can use to select the types of built distribution to generate: for example,

python setup.py bdist --format=zip

would, when run on a Unix system, create Distutils-1.0.plat.zip--again, this archive would be unpacked from the root directory to install the Distutils.

The available formats for built distributions are:

Format	Description	Notes
`gztar`	gzipped tar file (.tar.gz)	(1),(3)
`ztar`	compressed tar file (.tar.Z)	(3)
`tar`	tar file (.tar)	(3)
`zip`	zip file (.zip)	(4)
`rpm`	RPM	(5)
`pkgtool`	Solaris pkgtool
`sdux`	HP-UX swinstall
`rpm`	RPM	(5)
`wininst`	self-extracting ZIP file for Windows	(2),(4)

You don't have to use the bdist command with the --formats option; you can also use the command that directly implements the format you're interested in. Some of these bdist ``sub-commands'' actually generate several similar formats; for instance, the bdist_dumb command generates all the ``dumb'' archive formats (tar, ztar, gztar, and zip), and bdist_rpm generates both binary and source RPMs. The bdist sub-commands, and the formats generated by each, are:

Command	Formats
`bdist_dumb`	tar, ztar, gztar, zip
`bdist_rpm`	rpm, srpm
`bdist_wininst`	wininst

6.1 Creating dumb built distributions

** Need to document absolute vs. prefix-relative packages here, but first I have to implement it! **

6.2 Creating RPM packages

The RPM format is used by many popular Linux distributions, including Red Hat, SuSE, and Mandrake. If one of these (or any of the other RPM-based Linux distributions) is your usual environment, creating RPM packages for other users of that same distribution is trivial. Depending on the complexity of your module distribution and differences between Linux distributions, you may also be able to create RPMs that work on different RPM-based distributions.

The usual way to create an RPM of your module distribution is to run the bdist_rpm command:

python setup.py bdist_rpm

python setup.py bdist --formats=rpm

The former allows you to specify RPM-specific options; the latter allows you to easily specify multiple formats in one run. If you need to do both, you can explicitly specify multiple bdist_* commands and their options:

python setup.py bdist_rpm --packager="John Doe <[email protected]>" \
                bdist_wininst --target_version="2.0"

Creating RPM packages is driven by a .spec file, much as using the Distutils is driven by the setup script. To make your life easier, the bdist_rpm command normally creates a .spec file based on the information you supply in the setup script, on the command line, and in any Distutils configuration files. Various options and sections in the .spec file are derived from options in the setup script as follows:

RPM .spec file option or section	Distutils setup script option
Name	name
Summary (in preamble)	description
Version	version
Vendor	author and author_email, or & maintainer and maintainer_email
Copyright	licence
Url	url
%description (section)	long_description

Additionally, there many options in .spec files that don't have corresponding options in the setup script. Most of these are handled through options to the bdist_rpm command as follows:

RPM .spec file option or section	`bdist_rpm` option	default value
Release	release	``1''
Group	group	``Development/Libraries''
Vendor	vendor	(see above)
Packager	packager	(none)
Provides	provides	(none)
Requires	requires	(none)
Conflicts	conflicts	(none)
Obsoletes	obsoletes	(none)
Distribution	distribution_name	(none)
BuildRequires	build_requires	(none)
Icon	icon	(none)

Obviously, supplying even a few of these options on the command-line would be tedious and error-prone, so it's usually best to put them in the setup configuration file, setup.cfg--see section 4. If you distribute or package many Python module distributions, you might want to put options that apply to all of them in your personal Distutils configuration file (~/.pydistutils.cfg).

There are three steps to building a binary RPM package, all of which are handled automatically by the Distutils:

If you wish, you can separate these three steps. You can use the --spec-only option to make bdist_rpm just create the .spec file and exit; in this case, the .spec file will be written to the ``distribution directory''--normally dist/, but customizable with the --dist-dir option. (Normally, the .spec file winds up deep in the ``build tree,'' in a temporary directory created by bdist_rpm.)

** this isn't implemented yet--is it needed?! ** You can also specify a custom .spec file with the --spec-file option; used in conjunction with --spec-only, this gives you an opportunity to customize the .spec file manually:

> python setup.py bdist_rpm --spec-only
# ...edit dist/FooBar-1.0.spec
> python setup.py bdist_rpm --spec-file=dist/FooBar-1.0.spec

(Although a better way to do this is probably to override the standard bdist_rpm command with one that writes whatever else you want to the .spec file.)

6.3 Creating Windows Installers

Executable installers are the natural format for binary distributions on Windows. They display a nice graphical user interface, display some information about the module distribution to be installed taken from the metadata in the setup script, let the user select a few options, and start or cancel the installation.

Since the metadata is taken from the setup script, creating Windows installers is usually as easy as running:

python setup.py bdist_wininst

python setup.py bdist --formats=wininst

If you have a pure module distribution (only containing pure Python modules and packages), the resulting installer will be version independent and have a name like foo-1.0.win32.exe. These installers can even be created on Unix or MacOS platforms.

If you have a non-pure distribution, the extensions can only be created on a Windows platform, and will be Python version dependent. The installer filename will reflect this and now has the form foo-1.0.win32-py2.0.exe. You have to create a separate installer for every Python version you want to support.

The installer will try to compile pure modules into bytecode after installation on the target system in normal and optimizing mode. If you don't want this to happen for some reason, you can run the bdist_wininst command with the --no-target-compile and/or the --no-target-optimize option.

By default the installer will display the cool ``Python Powered'' logo when it is run, but you can also supply your own bitmap which must be a Windows .bmp file with the --bitmap option.

The installer will also display a large title on the desktop background window when it is run, which is constructed from the name of your distribution and the version number. This can be changed to another text by using the --title option.

The installer file will be written to the ``distribution directory'' -- normally dist/, but customizable with the --dist-dir option.

6.3.1 The Postinstallation script

Starting with Python 2.3, a postinstallation script can be specified which the --install-script option. The basename of the script must be specified, and the script filename must also be listed in the scripts argument to the setup function.

This script will be run at installation time on the target system after all the files have been copied, with argv[1] set to '-install', and again at uninstallation time before the files are removed with argv[1] set to '-remove'.

The installation script runs embedded in the windows installer, every output (sys.stdout, sys.stderr) is redirected into a buffer and will be displayed in the GUI after the script has finished.

Some functions especially useful in this context are available in the installation script.

directory_created(pathname)
file_created(pathname)

These functions should be called when a directory or file is created by the postinstall script at installation time. It will register the pathname with the uninstaller, so that it will be removed when the distribution is uninstalled. To be safe, directories are only removed if they are empty.

get_special_folder_path(csidl_string)

This function can be used to retrieve special folder locations on Windows like the Start Menu or the Desktop. It returns the full path to the folder. 'csidl_string' must be one of the following strings:

"CSIDL_APPDATA"

"CSIDL_COMMON_STARTMENU"
"CSIDL_STARTMENU"

"CSIDL_COMMON_DESKTOPDIRECTORY"
"CSIDL_DESKTOPDIRECTORY"

"CSIDL_COMMON_STARTUP"
"CSIDL_STARTUP"

"CSIDL_COMMON_PROGRAMS"
"CSIDL_PROGRAMS"

"CSIDL_FONTS"

Which folders are available depends on the exact Windows version, and probably also the configuration. For details refer to Microsoft's documentation of the SHGetSpecialFolderPath function.

create_shortcut(target, description, filename[, arguments[,
                workdir[, iconpath[, iconindex]]]])

This function creates a shortcut. target is the path to the program to be started by the shortcut. description is the description of the sortcut. filename is the title of the shortcut that the user will see. arguments specifies the command line arguments, if any. workdir is the working directory for the program. iconpath is the file containing the icon for the shortcut, and iconindex is the index of the icon in the file iconpath. Again, for details consult the Microsoft documentation for the IShellLink interface.