On Wed, Jan 15, 2020 at 06:05:42PM +0100, Miro Hrončok wrote:
> ### File types (and bytecode caches)
> The orthogonal dimension is the file type. Python standard library
> contains directories with both "extension modules" (written in C
> (usually) and compiled to `*.cpython-38-x86_64-linux-gnu.so` shared
> object file) and "pure Python" modules (written in Python and saved
> as `*.py` source file).
> Each pure Python module comes in 4 files:
> - `module.py` -- the source
> - `__pycache__/module.cpython-38.pyc` -- regular (not optimized) bytecode 
> cache
> - `__pycache__/module.cpython-38.opt-1.pyc` -- optimized bytecode cache 
> (level 1)
> - `__pycache__/module.cpython-38.opt-2.pyc` -- optimized bytecode cache 
> (level 2)

I suspect that the difference in speed between loading various .pyc
files is negligible. Do you have actual benchmarks for this?

> ### Solution 5: Stop shipping mandatory bytecode cache
> This solution sounds simple: We do no longer ship the bytecode cache
> mandatorily. Technically, we move the `.pyc` files to a subpackage
> of `python3-libs` (or three different subpackages, that is not
> important here). And we only *Recommend* them from `python3-libs` --
> by default, the users get them, but for space critical Fedora
> flavors (such as container images) the maintainers can opt-out and
> so can the powerusers.
> This would **save 18.6 MiB / 50%** -- quite a lot.
> However, as said earlier, if the bytecode cache files are not there,
> Python attempts to create them upon first import. That can result in
> several problems, here we will try to propose how to workaround
> them.

Below using a flag file in each __pycache__ directory is suggested.
What about a different route: having a flag file for all descendants
of a directory?

For example, /usr/lib/python3.8/.dont_write_bytecode
would cover all modules under /usr/lib/python3.8/.
If a .pyc file is present, python could still make use of it.

This would be a nicer solution because it wouldn't require modifying
individual packages, but would still avoid the selinux issues and
slowdowns from failed attempts to write the optimized files.
The __pycache__ files wouldn't need to exist at all.

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