[issue45020] Freeze all modules imported during startup.

[Guido van Rossum]

Guido van Rossum <guido at python.org> added the comment:

> It would be nice to freeze argparse.py and its dependencies.  For command-line tools, startup time is important.

I quickly checked, and argparse has at least these dependencies:

argparse
re
enum
types
operator
functools
collections
keyword
reprlib
sre_compile
sre_parse
sre_constants
copyreg
gettext

Raymond, do you think we should also freeze the dependencies of runpy (so "python -m <module>" also starts faster)?

That would be

runpy
importlib
warnings
importlib.machinery
importlib.util
importlib._abc
contextlib
collections
keyword
operator
reprlib
functools
types

(I didn't dedupe this from the previous list.)

With all these modules frozen we'd probably run more risk of two things:

- frozen modules don't have a __file__ (and are missing a few other, less commonly used, attributes)
- editing a frozen module requires rebuilding, or running with -X frozen_modules=off

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<https://bugs.python.org/issue45020>
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