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The Python C API should only define macros with a name starting wit Py #157695
Description
Currently, the Python C API defines 472 macros with a name which doesn't start with Py, PY, _Py or _PY prefix.
I propose adding a check to prevent adding new macros which doesn't respect this convention. Existing invalid names will be added to an ignore list for now.
Linked PRs
- gh-157695: Check that C API macros start with "Py" #157696
- gh-157695: Rename HAVE_FLOAT16 macro to _Py_HAVE_FLOAT16 #157752
- gh-157695: Rename HAVE_ICONV to _Py_HAVE_ICONV #157821
- gh-157695: Rename HAVE_ACOSPI to _Py_HAVE_ACOSPI #157858
- gh-157695: Rename HAVE_GETTID to _Py_HAVE_GETTID #157939
- gh-157695: Fix acospi() detection in configure.ac #157948
- gh-157695: Parse also _Py_HAVE_xxx variables in sysconfig #158926
Activity
vstinner commentedon Sep 17, 2026
The following Include/ header files are not included by Python.h and defines many macros which don't start with
Pyprefix:To clean up the C API, a simple move would be to move these header files to the internal C API. Problem: they are actually used in the wild (well, as usual ;-)).
I checked PyPI top 15,000 projects (at 2026-09-17) to find projects including these header files.
Projects (10) including opcode.h:
I found no project including errcode.h.
Projects (4) including osdefs.h:
Projects (169) including structmember.h:
For example, I searched for
include\s+["<]errcode\.h[">]for errcode.h include.vstinner commentedon Sep 17, 2026
This check is similar to "make smelly" which fails if libpython exports symbols with a name which doesn't start with "Py".
vstinner commentedon Sep 17, 2026
cc @encukou
vstinner commentedon Sep 17, 2026
See issue gh-149685 "Use _Py prefix for private C API added in 3.15" for a recent change (last May) about a similar issue.
gh-157695: Rename HAVE_FLOAT16 macro to _Py_HAVE_FLOAT16 (#157752)
gh-157695: Check that C API macros start with "Py" (#157696)
gh-157695: Rename HAVE_ICONV to _Py_HAVE_ICONV (#157821)
gh-157695: Rename HAVE_ACOSPI to _Py_HAVE_ACOSPI (#157858)
Locked-chess-official commentedon Sep 22, 2026
I have an immature idea: For configures, we can move the private configure macros into a new file named
pycore_pyconfig.hencukou commentedon Sep 22, 2026
structmember.hhas been deprecated in docs (which we now call soft deprectation) since 3.12. See also the comment in the header.IMO, exposing legacy non-
Py_-prefixed names via an opt-in#includeis perfectly fine.vstinner commentedon Sep 22, 2026
I'm not sure that autotools support multiple output files where some macros are defined in a file, and other macros are defined in another file.
configure.acusesAC_CONFIG_HEADERS([pyconfig.h]).gh-157695: Fix acospi() detection in configure.ac (#157948)
Locked-chess-official commentedon Sep 23, 2026
According to #141488 , the list of macros should be renamed anyway (it may has mistakes):
Details
HAVE_SYS_TYPES_HMS_WINDOWS
_POSIX_THREADS
WITH_PYMALLOC
WITH_MIMALLOC
HAVE_PTHREAD_H
DYNAMIC_ANNOTATIONS_ENABLED
HAVE_SYS_STAT_H
S_IFMT
S_IFLNK
S_ISREG
S_ISDIR
S_ISCHR
S_ISLNK
HAVE_FORK
STACKLESS
SEP
MAXPATHLEN
DELIM
_BSD_WCHAR_T_DEFINED_
NCURSES_VERSION
MVWDELCH_IS_EXPRESSION
CURSES_MODULE
WITH_DTRACE
WITH_DOC_STRINGS
UCHAR_MAX
HAVE_LONG_LONG
HAVE_PY_SSIZE_T
SIGNED_RIGHT_SHIFT_ZERO_FILLS
INT_MAX
LONG_MAX
LONG_MIN
LONG_BIT
WORDS_BIGENDIAN
WITH_THREAD
USE_STACKCHECK
SIZEOF_WCHAR_T
HAVE_USABLE_WCHAR_T
HAVE_WCHAR_H
vstinner commentedon Sep 23, 2026
I replaced
AC_CHECK_FUNCS_ONCE(acospi asinpi atanpi atan2pi cospi sinpi tanpi)withPY_CHECK_FUNC_PRIVATE([acospi])(and similar call for the other functions) wherePY_CHECK_FUNC_PRIVATE()is a new function based onPY_CHECK_FUNC().I expected
PY_CHECK_FUNC()to be the same asAC_CHECK_FUNC(), but it works differently.AC_CHECK_FUNC()doesn't need to include the system header file declaring the function. It only checks if the C library has a symbol with the expected name (it doesn't check the API).PY_CHECK_FUNC()requires to include the right header file, otherwise the function is not detected.I had to fix configure.ac to use
PY_CHECK_FUNC_PRIVATE([acospi], [@%:@include <math.h>])instead.The problem is that it's not always easy to pick the right header file to get a function, or different operating systems can use different header files.
It would be nice to have a function similar to
AC_CHECK_FUNC()(only check if the function exists, don't check its API), but define_Py_HAVE_xxxmacro instead ofHAVE_xxx.For now, I put my #157939 PR on hold until I better understand this issue.
Merge branch 'main' into fix-iconv-stateful-incremental
gh-157695: Parse also _Py_HAVE_xxx variables in sysconfig (#158926)
[3.15] gh-158893: Make os.strerror() thread-safe (#159120)
[3.15] pythongh-158893: Make os.strerror() thread-safe (python#159120)
[3.14] gh-158893: Make os.strerror() thread-safe (#159120) (#159145)