[csw-maintainers] Python 2.7

[Maciej (Matchek) Bliziński]

2013/7/25 Peter FELECAN <pfelecan at opencsw.org>
>
> As an aside, this brings up the question: why do we need to
> compile at installation time and not deliver the pre-compiled bits; is
> the p-code not portable on different architectures?

The Debian Python policy doesn't provide the reasons why they do it that way.
http://www.debian.org/doc/packaging-manuals/python-policy/ch-module_packages.html#s-byte_compilation

According to my own web searching, the *.pyc files are
Python-version-dependent according to this entry on stackoverflow:
http://stackoverflow.com/questions/2263356/are-python-2-5-pyc-files-compatible-with-python-2-6-pyc-files

They don't provide sources, so I couldn't quickly verify it. I did see
an example where the Python version has been shown to be encoded
inside a *.pyc file. I'm not sure how Python handles version
mismatches. I'm expecting that it reads the file, deserializes it,
check the version and if a mismatch is detected, it discards the *.pyc
file and compiles the *.py file. This would mean that a *.pyc file is
always useless for one of the two installed Python versions.

I looked at the Debian pyshared solution by poking an installed
system. The quick summary is:

- /usr/share/pyshared contains the .py files and is not a member of sys.path
- for each Python version a /usr/lib/pythonX.Y/dist-modules directory
exists and is a member of sys.path
- when a module is installed, symlinks from
/usr/lib/pythonX.Y/dist-modules to respective entries in
/usr/share/pyshared are made. They are exclusively file symlinks, and
never directory symlinks.
- the *.py files are compiled once per Python version, and *.pyc files
live in the /usr/lib/pythonX.Y/dist-modules directory tree

Sounds very reasonable to me. Somebody has to implement it for us though.

Maciej