[issue42902] a python embedded program may load "C:\Lib\os.py" on windows system

[STINNER Victor]

STINNER Victor <vstinner at python.org> added the comment:

Hum. The code in Python 3.8 is complicated. When Py_SetPath() is called, Python starts by computing the Python Path Configuration because of:

    /* Getting the program full path calls pathconfig_global_init() */
    wchar_t *program_full_path = _PyMem_RawWcsdup(Py_GetProgramFullPath());

The result is stored info _Py_path_config. Then Py_SetPath() overrides program_full_path, prefix, exec_prefix and module_search_path of _Py_path_config.

When Python reachs Py_Initialize(), PyConfig_Read() does not compute the Python Path Configuration, but copies what comes from _Py_path_config.

--

I changed the code a lot of Python 3.10 to make it more deterministic and simpler. For example, Py_SetPath() no longer computes the Python Path Configuration.

commit ace3f9a0ce7b9fe8ae757fdd614f1e7a171f92b0
Author: Victor Stinner <vstinner at python.org>
Date:   Tue Nov 10 21:10:22 2020 +0100

    bpo-42260: Fix _PyConfig_Read() if compute_path_config=0 (GH-23220)
    
    Fix _PyConfig_Read() if compute_path_config=0: use values set by
    Py_SetPath(), Py_SetPythonHome() and Py_SetProgramName(). Add
    compute_path_config parameter to _PyConfig_InitPathConfig().
    
    The following functions now return NULL if called before
    Py_Initialize():
    
    * Py_GetExecPrefix()
    * Py_GetPath()
    * Py_GetPrefix()
    * Py_GetProgramFullPath()
    * Py_GetProgramName()
    * Py_GetPythonHome()
    
    These functions no longer automatically computes the Python Path
    Configuration. Moreover, Py_SetPath() no longer computes
    program_full_path.

This change is a little bit backward incompatible, even I would not recommend to call Py_GetXXX() functions before Py_Initialize() in Python 3.8 or 3.9.

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