8000 `sysconfig.get_config_var("Py_DEBUG")` is not picked up on Windows builds · Issue #133878 · python/cpython · GitHub
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sysconfig.get_config_var("Py_DEBUG") is not picked up on Windows builds #133878

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cctv130 opened this issue May 11, 2025 · 12 comments
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sysconfig.get_config_var("Py_DEBUG") is not picked up on Windows builds #133878

cctv130 opened this issue May 11, 2025 · 12 comments
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OS-windows stdlib Python modules in the Lib dir topic-sysconfig type-bug An unexpected behavior, bug, or error

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@cctv130
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cctv130 commented May 11, 2025

I used the PCbuild\build.bat -e -d -p x64 command to build, but when I print PY_DEBUG, it returns None.
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@picnixz
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picnixz commented May 11, 2025 •
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@zooba should a build with -d be expected to define Py_DEBUG as well? We have this

/* _DEBUG implies Py_DEBUG */
#ifdef _DEBUG
#  define Py_DEBUG 1
#endif

but it appears that sysconfig can't pick this up.

@picnixz picnixz changed the title how to properly enable and use Py_DEBUG on Windows？ sysconfig.get_config_var("Py_DEBUG") is not picked up on Windows builds May 11, 2025
@picnixz
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picnixz commented May 11, 2025

@cctv130 Does it work better if you're using Python 3.13 or Python 3.14?

@picnixz picnixz added type-bug An unexpected behavior, bug, or error stdlib Python modules in the Lib dir and removed extension-modules C modules in the Modules dir labels May 11, 2025
@StanFromIreland
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It should, as per the docs:

cpython/PCbuild/readme.txt

Lines 35 to 42 in 9b9cdb6

Debug
Used to build Python with extra debugging capabilities, equivalent
to using ./configure --with-pydebug on UNIX. All binaries built
using this configuration have "_d" added to their name:
python310_d.dll, python_d.exe, parser_d.pyd, and so on. Both the
build and rt (run test) batch files in this directory accept a -d
option for debug builds. If you are building Python to help with
development of CPython, you will most likely use this configuration.

@cctv130
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cctv130 commented May 11, 2025

@StanFromIreland
On the Windows platform, the compilation method is different from Linux; the ./configure command is not supported on Windows.

@cctv130
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cctv130 commented May 11, 2025

@zooba should a build with -d be expected to define Py_DEBUG as well? We have this

/* _DEBUG implies Py_DEBUG */
#ifdef _DEBUG
#  define Py_DEBUG 1
#endif

but it appears that sysconfig can't pick this up.

If that's the case, then the _DEBUG flag must be added to the MSVC compiler.

@picnixz
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picnixz commented May 11, 2025

_DEBUG is already MSVC-specific; I think it's more a sysconfig issue

@cctv130
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cctv130 commented May 11, 2025

@picnixz
If that's the case, we can use CMake configuration instead of configure to support more platforms.

@picnixz
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picnixz commented May 11, 2025 •
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Changing the build configuration and how it's being built is out-of-scope of this issue and this is not some 8000 thing we want to do now. In this case, we need to figure out why sysconfig doesn't pickup Py_DEBUG or whether it's not set.

@XuehaiPan
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XuehaiPan commented May 11, 2025 •
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I used the PCbuild\build.bat -e -d -p x64 command to build, but when I print PY_DEBUG, it returns None. Image

The Py_DEBUG key in sysconfig.get_config_vars() on Windows was added in #131799, which first appeared in Python 3.14.0b1.

As the screenshot shows, you are using Python 3.12.10.

@zooba
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zooba commented May 11, 2025

Yeah sysconfig on Windows doesn't pick up anything automatically, as there's no Makefile for it to parse. XuehaiPan added some variables for 3.14 - prior to that, you needed to look for debug-only attributes (e.g. sys.gettotalrefcount is a popular choice) or Path(sys.executable).match("*_d.exe").

@cctv130
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cctv130 commented May 12, 2025

thanks

@cctv130 cctv130 closed this as completed May 12, 2025
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