Python in Debian
Software written in the Python programming language is executed by Python interpreter and is usually compiled into platform independent bytecode files to increase performance. Thus software that written in pure Python can be distributed as source code or as compiled bytecode. The latter is similar to Java. Unfortunately, compiled bytecode files are incompatible from Python version to Python version. Certain Debian system may have several Python versions available, so to avoid distributing several packages for each version, Debian Policy makes sure that Python code is distributed in clear form and compiled only during installation process on target system. Python is able to compile and write bytecode *.pyc files alongside with *.py sources when *.py is executed, but insufficient permissions may not allow it to write in corresponding directories, so to avoid drop-down in performance compiling is done during installation.
The so-called C-Python interpreter is a software package containing both the compiler and the bytecode interpreter used to execute Python files. Within the Debian project the Python compiler/interpreter package is maintained by a developers team known as pkg-python. Python modules and extensions are maintained by individual developers and by a coordinated group called Debian Python Modules Team. There are also Python applications that are maintained by a separate Python Applications Packaging Team.
Supported Python Versions
Debian's latest release Lenny contains multiple Python versions: 2.5 (the default) and 2.4.
Debian Python Policy for Python developers
Text of Debian Python Policy describes conventions for packaging and distributing Python code in Debian. The official text is located at http://www.debian.org/doc/packaging-manuals/python-policy/ but as a matter of fact many find it outdated and incomplete, so feel free to ask any questions on firstname.lastname@example.org mailing list and contribute to DebianPython/Tutorial.
The text of current official policy can be summarized as follows:
- Debian installation may have multiple Python versions
- Modules should be installed to /usr/lib/pythonX.Y/site-packages
- Bytecompilation should occur in post installation step (postinst), bytecompiled files should be removed in prerm
- /etc/python/debian_config has option to control byte compilation
Current Policy shortcomings
Even though DebianPython/NewPolicy is called New, it is still doesn't reflect the real state of affairs in Python packaging.
- (ambiguous) It does it's best to explain what should be done, it fails to guide people how it should be done.
- (obscure) It doesn't explain the reasons behind some of the rules.
- (complicated) It requires that Python developers should be familiar with Debian tools.
That's why the state of support of Python packages in Debian is not super and a separate DebianPython/Tutorial is really needed.