GH-109653: Defer import of importlib.metadata._adapters - #109829

I notice that the description here only mentions importlib.metadata, but this change also affects importlib.resources. Both packages have _adapters modules.

Can you confirm how much of the speedup is achieved by each of the two changes? How is timing benchmarked (is it as simple as py -m timeit 'import typing')?

How is timing benchmarked

$ python -X importtime -Sc 'import importlib.metadata' 2> importlib_metadata.log
$ cat importlib_metadata.log
$ tuna importlib_metadata.log

The tuna viewer is optional, often I just read the text log.

A

Can you confirm how much of the speedup is achieved by each of the two changes?

I'll try and come back with some timings

A

Here's some timings on macOS (non-debug build with --enable-optimizations --with-lto), running this three times, timings give from third run so everything's been imported at least once:

./python.exe -X importtime -Sc 'import importlib.metadata' 2> importlib_metadata.log && tuna importlib_metadata.log

Baseline with main (86e5e06)

importlib.metadata: 0.048 s

Details

Deferring in Lib/importlib/metadata/__init__.py

importlib.metadata: 0.040 s

Details

Deferring in Lib/importlib/resources/_common.py

importlib.metadata: 0.037 s

Details

Deferring in both Lib/importlib/metadata/__init__.py and Lib/importlib/resources/_common.py

importlib.metadata: 0.030 s

Details

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

Cherry-picked to python/importlib_metadata@6673723baa and python/importlib_resources@ca03a4df06.