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Talk on Packaging 2010-03-13
These are the notes from a talk at Meeting20100313 by David Fraser on Python packaging for Fedora, RHEL, Windows, etc
General Packaging
- We have source code for Python libraries, applications and tools
- These have dependencies on other Python libraries, as well as non-Python libraries (database drivers etc)
- We need users to run our applications etc on various platforms
Terms of Endearment
- Distribution here refers to a built Python thing
- Distro refers to a Linux distribution
- Package refers to a Python package (a module with submodules)
- rpm refers to a package file in the RPM format (to distinguish from Python packages)
Distutils
- distutils is the standard Python packaging system
- Various extensions exist that augment its capabilities, and because you use Python, you can do that to
- Input: you write a
setup.py
script (and optionally asetup.cfg
configuration file) that specifies:- Package metadata (name, version, authorship, licensing, dependencies, etc)
- Package contents (pure python modules/packages, extensions, executable Python scripts, data - non-code that needs to be in the package, scripts that aid installation etc)
- Output: running
setup.py
supports various commands that produce different outputs:sdist
produces a source distribution - it helps if you can regenerate the distribution from a clean source distributionMANIFEST.in
template->
MANIFEST
list of files to include - these are not regenerated automatically by default (--force-manifest
)
bdist
contains a generic built installation (but I've hardly ever seen it used as it's not a useful package format)bdist_rpm
generates RPM and SRPM package filesbdist_wininst
produces a Windows executable installer that will install the distribution into an existing Python installation- The output generally gets put in a
dist
subdirectory
- Commands include the above output commands, as well as intermediate commands that are run on the way to producing the above
- Each command can have command-specific options (as well as the generic options passed to
setup.py
) - Options can be specified per-command either in
setup.py
or insetup.cfg
, or on the command-line build
is an intermediate command which runs:build_py
for pure modules (simple copy to the build directory)build_ext
for compiling C/C++ extensions, links them to build directorybuild_clib
for building C/C++ librariesbuild_scripts
which copies them and alters the#!
line
install
then installs everything from the build directory to the target (separate steps likebuild
)clean
cleans up the build directory- You can also
register
the command with the Python package index, andupload
it
- Each command can have command-specific options (as well as the generic options passed to
- Scripts can include things to run (which can be installed into the path), as well as a post-installation/pre-removal script
- Things to consider:
- If you've got a bunch of related files, should they be in a package? Otherwise they can clutter the standard Python
site-packages
directory - Can you cleanly regenerate your source distribution from itself
- Package dependencies: a distribution can provide, require or obsolete packages
- Consider creating distributions on the same platform as you're targetting, or from other platforms, or both
- How are you going to build your distribution for different platforms?
- How are you going to deliver your distribution to people on different platforms, including dependencies?
- How will your distribution interact with the native packaging on the target platforms (if any)
- If you've got a bunch of related files, should they be in a package? Otherwise they can clutter the standard Python
The world of eggs
setuptools is a set of extensions to distutils
that try and bring it into the modern age:
- Adds proper dependency support to Python packages
- Lots of surrounding tools -
easy_install
,pkg_resources
etc - very simple ways of installing stuff from the standard Python repositorya - Lots more tools being built around this format
- Simply import
setuptools
instead ofdistutils
- Does not integrate directly with distros' packaging systems
- Supports parallel versions of the same library reasonably well (you can
require
a specific version and use it even if a different one is present - however conflicts can arise) - Not that good at uninstallation etc
The world of RPM
- RPM is a packaging format that originated with RedHat, and is now used in RHEL/CentOS/Fedora, SUSE Enterprise/openSUSE, Mandriva as well as being part of the Linux Standard Base
- Input: A
.spec
file defines a rpm's metadata, how to build both a source and a binary rpm, what sources to use, patches to apply, etc, etc- This is a more data-driven format than
setup.py
- The
.spec
file contains a header section for general information as well as- script sections for
%prep
aring the build,%setup
(unpacking the source and packaging),%build
ing the source,%install
ing (into aBUILD_ROOT
directory),
%checking the results, and
%clean`ing up %pre
and%post
installation scripts, and%preun
and%postun
uninstallation scripts- A list of the
%files
included in the rpm (including categories like%doc
umentation, and file attributes) - A
%changelog
- script sections for
- Support for macros, including shell execution to define macros
- Support for subpackages - multiple rpms can be built from the same
.spec
file
- This is a more data-driven format than
- From
distutils
,bdist_rpm
generates a source distribution, creates a spec file, generates a source rpm from that, and then a binary rpm - What's really useful about
rpm
is dependency based on repositories- Different distros have different tools for this, and they vary in capability between releases -
RHEL/CentOS/Fedora
use yum - There isn't that much functional difference between the
.deb
format/the.rpm
format, andapt-get
/yum
etc - for the user. There is for the packager... - You can specify dependencies as options to
bdist_rpm
(insetup.py
,setup.cfg
or on the commandline) - they don't seem to get included from the normal package metadata
- Different distros have different tools for this, and they vary in capability between releases -
- Distros/repositories have different standards and requirements for inclusion of rpms and
.spec
filesbdist_rpm
's automatically generated.spec
files will generally not meet these requirements- The general feeling is that for inclusion into a distro,
.spec
files should be hand-generated and maintained - Are you targeting your rpms for inclusion in a Linux distro? Read and follow the rules and follow the procedures...
- Otherwise you may be happy with the standard
distutils
stuff - Generally packages using
setuptools
can install their.egg
information alongside the source code and include that in the rpm
- Targetting older distros can be tricky if you are using lots of modern Python stuff
- Distros have their own version of Python - you may require a newer one. Typically this can be installed alongside as something like
python25.rpm
- often these rpms exist, sometimes you have to rebuild them - In that case you will need to package all the dependencies for the new Python - usually called
python25-babel
etc - Doing this on multiple distros can be tiring. Since you're not targetting inclusion in the old distros, try and get away with murder (or at least, functional packages rather than beautifully crafted ones)
- Distros have their own version of Python - you may require a newer one. Typically this can be installed alongside as something like
- We have a tool called centuryegg for targetting older distros
- This is currently reasonably specific to our set of requirements
- Order of priority:
- Use existing
rpm
s from the target distro - Backport
rpm
s from newer releases of the target distro - Spin our own
rpm
s from the eggs in PyPI
- Use existing
- Target is to be able to automatically source and download all the requirements from a simple list, generate the rpms, and upload them into a repository
- We should make it more generic - is anyone interested?
- Generating your own repository
- You will generally need different repositories for different distros and versions (even apparently equivalent ones like
RHEL4
/CentOS 4
) - Usually this just involves compiling (strongly recommend doing this on the target distro - we had strange crashes due to minor library versioning differences etc)
- You then just need to run something like
createrepo
and put the files in a web space
- You will generally need different repositories for different distros and versions (even apparently equivalent ones like
The world of Windows
bdist_win32
is fine for lots of purposes - especially if distributing packages to other developersbdist_msi
has now also been added, that produces packages in Windows installer's MSI format (this is also used to produce the python msi itself)- For distributing applications, most Windows users expect a single install, and may be confused by having the Python runtime environment set up on their machine with lots of libraries
- py2exe is the most popular of a variety of tools for producing a frozen Python distribution on Windows:
- An extension to
distutils
- Packages up the Python runtime, and a set of Python packages, modules, extensions, scripts and data, into a target directory
- Scripts are converted to stub
win32
executables that load the Python dll and execute some code - Automatic search for Python library dependencies (by scanning your source code for
import
statements), as well as manual specification of requirements - All the libraries you depend on need to be included - sometimes having things installed as
eggs
on the build environment can produce problems - Running in frozen mode often requires some changes to the underlying code for compatibility - location of files etc - lots of tips on the wiki site
- An extension to
- It's fairly common to use InnoSetup to produce an installer containing all the required files, Start menu items, etc
Putting it all together
- It makes life easier if you can do all the above, and whatever other targets you require, from the same
setup.py
script - Separate out options for the different commands as much as possible
- We found we had to hack
distutils
a lot with derived code to make it all work
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Sample library upstream source
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hellopy_1.9-1.debian.tar.gz
(2.3 KB
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Sample library Debian packaging changes
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hellopy_1.9-1.dsc
(1.0 KB
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Sample library Debian package description
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