sysconfig.get_platform() could return wrong value because sys.version is truncated

[char101]

Bug report

Bug description:

On Windows, sysconfig.get_platform() checks for the string amd64 (for 64 intel) in sys.version.

This is the value of sys.version for python 3.14.3 (64 bit) compiled with clang 22.1.0

>>> sys.version
'3.14.3 (main, Mar  2 2026, 14:42:29) [Clang 22.1.0 (https://github.com/llvm/llvm-project 4434dabb69916856b824f68a64b0'
>>> sysconfig.get_platform()
'win32'
>>> import platform
>>> platform.architecture()[0]
'64bit'

As visible, there is no amd64 in sys.version, because it is truncated. This causes problem when installing native package using pip because cp314-cp314-amd64 is not in the list of supported tags. Instead, the supported tags list become

Compatible tags: 48
  cp314-cp314-win32
  cp314-abi3-win32
  cp314-none-win32
  cp313-abi3-win32
  cp312-abi3-win32
  cp311-abi3-win32
  cp310-abi3-win32
  cp39-abi3-win32
  cp38-abi3-win32
  cp37-abi3-win32
  cp36-abi3-win32
  cp35-abi3-win32
  cp34-abi3-win32
  cp33-abi3-win32
  cp32-abi3-win32
  (truncated)

CPython versions tested on:

3.14

Operating systems tested on:

Windows

Linked PRs

• gh-145410: Add _sysconfig.get_platform() function #146145
• gh-145410: Use _sysconfig.get_platform() in the platform module #146148
• gh-145410: Fix sysconfig.get_platform() for truncated sys.version on Windows #146146

[char101]

With regard to clang, in getcompiler.c

#if defined(__clang__)
#define COMPILER "[Clang " __clang_version__ "]"

Where __clang_version__ is documented as:

__clang_version__

    Defined to a string that captures the Clang marketing version, including the Subversion tag or revision number, e.g., “1.5 (trunk 102332)”.

I think a safer implementation would be

#if defined(__clang__)
#define COMPILER "[Clang " __clang_major__ "." __clang_minor__ "." __clang_patchlevel__ "]"

[encukou]

This looks like an artifact of clang being untested & unsupported on Windows.

Does the full __clang_version__ include the string "amd64"?

[char101]

It contains AMD64, as defined in PC/pyconfig.h, but will be truncated if __clang_version__ is long.

cpython/PC/pyconfig.h

Line 161 in 201d251

#define _Py_COMPILER ("[Clang " __clang_version__ "] 64 bit (AMD64) with MSC v." _Py_STRINGIZE(_MSC_VER) " CRT]")

I think for future proofing, it is better for the sysconfig module not to depend on sys.version because it is fragile. The plaform module seems to be a better choice.

[encukou]

I also wouldn't be against increasing the limits in getversion.c.

[zooba]

sysconfig should rely on _sysconfig if it needs access to something known at compile time.