[Cython] cython-0.23 monkey-patches stdlib?

[Stefan Behnel]

Neal Becker schrieb am 06.06.2015 um 20:25:
> According to
> https://github.com/cython/cython/blob/master/CHANGES.rst
> 
> the default build would attempt to modify python stdlib files?

No. Glad you asked, that might not be clear.

It will not modify the *files*, only the content of the modules after
importing them. It adds the missing ABCs to the collections.abc module and
registers Cython's own types with them *at runtime*. Here's what it does:

https://github.com/cython/cython/blob/bb0dec2/Cython/Utility/Coroutine.c#L1322

This is a bit fragile, like all monkey-patching. As long as things get
imported in the right order, it works. But if you import asyncio before a
Cython module that adds the ABCs, it may already have decided that the ABCs
don't exist and won't use them. That's controllable on user application
side, though.

Also, the first patcher necessarily wins, so if there will ever be updates
to the ABCs, old Cython modules would still patch in the old versions when
imported first. They should tend to be quite stable, though.

In any case, this will get better over time as more code switches to Py3.5
and later.

Stefan