sysconfig.get_config_var("Py_DEBUG") is not picked up on Windows builds

I used the PCbuild\build.bat -e -d -p x64 command to build, but when I print PY_DEBUG, it returns None.

@zooba

@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.

@cctv130

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

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.

@StanFromIreland

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

@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.

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

@picnixz

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

Changing the build configuration and how it's being built is out-of-scope of this issue and this is not something 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.

I used the PCbuild\build.bat -e -d -p x64 command to build, but when I print PY_DEBUG, it returns None.

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.

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").

thanks

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`sysconfig.get_config_var("Py_DEBUG")` is not picked up on Windows builds #133878

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	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.

sysconfig.get_config_var("Py_DEBUG") is not picked up on Windows builds #133878

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StanFromIreland commented on May 11, 2025

picnixz commented on May 11, 2025

picnixz commented on May 11, 2025

StanFromIreland commented on May 11, 2025

cctv130 commented on May 11, 2025

cctv130 commented on May 11, 2025

picnixz commented on May 11, 2025

cctv130 commented on May 11, 2025

picnixz commented on May 11, 2025

XuehaiPan commented on May 11, 2025

zooba commented on May 11, 2025

cctv130 commented on May 12, 2025

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`sysconfig.get_config_var("Py_DEBUG")` is not picked up on Windows builds #133878