libregrtest: Reduce number of imports at startup

[vstinner]

Currently, when a test is run by ./python -m test (...), the test starts with 170 modules already imported. The problem is that imports can have side effects and I would prefer to start tests in a "minimal environment".

Running a test with ./python -m test (...) only imports 164 modules.

Example by adding Lib/test/test_x.py:

import sys
print(len(sys.modules))

Output:

vstinner@mona$ ./python -m test test_x
170

vstinner@mona$ ./python -m test -j1 test_x
164

I propose to try to make more imports lazy: only import the module the first time that it's needed, tests are rarely "performance sensitive". It may improve the "startup time".

Linked PRs

• gh-111881: Import doctest lazily in libregrtest #111884
• gh-111881: Use lazy import in test.support #111885
• gh-111881: Import lazily linecache in traceback #111886
• gh-111881: Use lazy import in unittest #111887
• gh-111881: Use lazy import in doctest #111888
• gh-111881: Import _sha2 lazily in random #111889
• [3.12] gh-111881: Use lazy import in test.support (#111885) #111890
• [3.12] gh-111881: Import doctest lazily in libregrtest (GH-111884) #111893
• [3.11] gh-111881: Import doctest lazily in libregrtest (GH-111884) #111894
• [3.11] gh-111881: Use lazy import in test.support (#111885) (#111890) #111902
• gh-111881: Import lazily zipfile in support.script_helper #112172

[arneja-arnav]

May I work on this issue? would love to take a crack at it.

[vstinner]

May I work on this issue? would love to take a crack at it.

Yes, you can review proposed PRs and help to get them merged.

[vstinner]

I lost track of this change, so I just close it.