Description

vstinner

opened on Sep 14, 2026

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Currently, arguments of Py_MIN(), Py_MAX() and Py_ABS() macros are evaluated twice. It's inefficient. We can do better using typeof(). I propose adding a typeof() implementation for these macros.

See also:

• GCC typeof: https://gcc.gnu.org/onlinedocs/gcc/Typeof.html
• n3543 "Add type-safe minimum and maximum type-generic macros" proposition for the C standard.

Linked PRs

• gh-157495: Implement Py_MIN() and Py_MAX() using typeof() #157496
• gh-157495: Avoid Py_MIN()/Py_MAX() side effects #157591

Activity

1. vstinner

   added

   topic-C-API

   on Sep 14, 2026
2. picnixz

   added

   type-featureA feature request or enhancementA feature request or enhancement

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Sep 14, 2026
3. StanFromIreland

   added

   type-refactorCode refactoring (with no changes in behavior)Code refactoring (with no changes in behavior)

   and removed

   type-featureA feature request or enhancementA feature request or enhancement

   on Sep 14, 2026
4. serhiy-storchaka commented on Sep 14, 2026

   

   serhiy-storchaka

   on Sep 14, 2026

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   How would it work in C++?
5. vstinner commented on Sep 14, 2026

   

   vstinner

   on Sep 14, 2026

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   How would it work in C++?

   The current implement (without typeof) is used for C++.

   Statement expressions are not allowed in C++. My PR adds explicit tests on Py_MIN() and Py_MAX() in test_cppext: so the macros are tested in C++ with different compiler flags, with and without the limited C API.

   typeof() cannot be used on MSVC neither because statement expression is a GNU extension which is only supported by GCC and clang (not by MSVC).
6. skirpichev commented on Sep 15, 2026

   

   skirpichev

   on Sep 15, 2026

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   Currently, arguments of Py_MIN(), Py_MAX() and Py_ABS() macros are evaluated twice. It's inefficient.

   Does it matter for default builds, when optimizations turned on?
7. vstinner commented on Sep 15, 2026

   

   vstinner

   on Sep 15, 2026

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   The documentation of Py_MIN(), Py_MAX() and Py_ABS() macros says:

   The argument may be evaluated more than once. Consequently, do not pass an expression with side-effects directly to this macro.

   min=Py_MIN(var, expensive_func()) should be replaced with result=expensive_func(); min=Py_MIN(var, result) for example.

   Since my proposal change is only available on some compilers (GCC and clang, not on MSVC), Python code base should continue to follow the documentation advices.

   I didn't check the 221 calls to these macros (git grep -E '(Py_MIN|Py_MAX|Py_ABS)\('|wc -l).
8. vstinner

   added a commit that references this issue on Sep 15, 2026

   pythongh-157495: Avoid Py_MIN()/Py_MAX() side effects

   e70baf3
9. vstinner commented on Sep 15, 2026

   

   vstinner

   on Sep 15, 2026

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   I didn't check the 221 calls to these macros (git grep -E '(Py_MIN|Py_MAX|Py_ABS)('|wc -l).

   Ok, I checked Py_MIN/MAX/ABS calls in the Python code base and I found a few calls which are inefficient. I wrote this PR gh-157591 to fix them.
10. vstinner

    added 2 commits that reference this issue on Sep 15, 2026

    gh-157495: Implement Py_MIN/MAX/ABS using typeof() (#157496)

    e2ca4dc

    gh-157495: Avoid Py_MIN()/Py_MAX() side effects (#157591)

    ba91215
11. vstinner

    closed this as completedon Sep 18, 2026
12. ZeroIntensity

    added a commit that references this issue on Nov 12, 2026

    [3.15] gh-161712: Read the clock once in `ThreadHandle_join()` (GH-16…

    88d137a

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