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Speed-up build by avoiding a expensive operation #3395

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Merged
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Jul 4, 2022
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Speed-up build by avoiding a expensive operation #3395

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199deb1
build_meta: execute code directly
abravalheri Jun 20, 2022
e1c6701
Add news fragment
abravalheri Jun 20, 2022
241b529
Remove outdated part in news fragment
abravalheri Jul 4, 2022
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2 changes: 2 additions & 0 deletions changelog.d/3395.change.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Included a performance optimization: ``setuptools.build_meta`` no longer tries
to :func:`compile` the setup script code before :func:`exec`-ing it.
2 changes: 1 addition & 1 deletion setuptools/build_meta.py
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Expand Up @@ -171,7 +171,7 @@ def run_setup(self, setup_script='setup.py'):
with _open_setup_script(__file__) as f:
code = f.read().replace(r'\r\n', r'\n')

exec(compile(code, __file__, 'exec'), locals())
exec(code, locals())
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@abravalheri abravalheri Jun 20, 2022

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The only difference I can think here is that if the setup script has a syntax error, compile would fail so no instruction gets executed. I don't know how exec works, but it could be the case it gets to execute something before failing... I don't think this is relevant though because the PEP 517 hooks are supposed to be executed in isolated subcommands, so it is fine for the hook to crash.

However, I might be failing to see other problems...

Alternatively we could also try.

 try: exec(code, locals()) except Exception: exec(compile(code, __file__, 'exec'), locals())
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@jaraco jaraco Jul 4, 2022

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It's my understanding that if there is a syntax error, nothing will ever be executed, so no concerns here.
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@Joshix-1 Joshix-1 May 31, 2025

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An important difference is that ­— when an exception gets raised — the stacktrace is now broken. The second argument to compile tells python where to find the source code when displaying the stacktrace. That's exactly what #3577 wanted to improve.

Calling compile before exec doesn't seem to have any noticeable effect on performance:

$ python -m timeit -s 'code = "1 + 1 #" + "A"*10000' 'exec(code)' 20000 loops, best of 5: 10.7 usec per loop $ python -m timeit -s 'code = "1 + 1 #" + "A"*10000' 'exec(compile(code, __file__, "exec"))' 20000 loops, best of 5: 10.7 usec per loop

I don't see how that could make any difference. To execute code the code needs to get compiled before. It doesn't matter if compile gets executed explicitly.

def get_requires_for_build_wheel(self, config_settings=None):
return self._get_build_requires(
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