This only helps the -S startup because site.py imports os.py which also imports _collections_abc.

I think it's pretty defensible to lazy-import here as well as in os.py though; the import is only needed for runtime isinstance() checks on these protocols, and many users will use them without ever needing the isinstance() call.

I believe it is related to #118761

Confirmation on controlled benchmarking hardware that this is effective: https://github.com/faster-cpython/benchmarking-public/blob/main/results/bm-20250425-3.14.0a7%2B-9fc1238/bm-20250425-linux-x86_64-mdboom-python_startup_time-3.14.0a7%2B-9fc1238-vs-base.svg

@mdboom are you happy to merge this? It's still 'draft'.

A

If we merge this, let's try to make it so _collections_abc isn't imported on normal (without -S) startup too, so this helps in a bit more realistic cases. It should be easy to defer the import in os.py.

It turns out it's not actually feasible to make os.py also lazy-import _collections_abc, because os.Environ inherits from _collections_abc.MutableMapping.

That means (if we merge #132957) this PR only helps in the case where the user used -S and imports io, but not os or pretty much anything else. I feel that's unlikely enough that it's not worth making this change.

It turns out it's not actually feasible to make os.py also lazy-import _collections_abc, because os.Environ inherits from _collections_abc.MutableMapping.

That means (if we merge #132957) this PR only helps in the case where the user used -S and imports io, but not os or pretty much anything else. I feel that's unlikely enough that it's not worth making this change.

Yeah, I agree. I think #132957 is the better solution. Closing.