Author vstinner
Recipients christian.heimes, eryksun, houjingyi233, paul.moore, steve.dower, tim.golden, vstinner, zach.ware
Date 2021-01-12.17:24:20
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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 <>
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_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

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.
Date User Action Args
2021-01-12 17:24:20vstinnersetrecipients: + vstinner, paul.moore, christian.heimes, tim.golden, zach.ware, eryksun, steve.dower, houjingyi233
2021-01-12 17:24:20vstinnersetmessageid: <>
2021-01-12 17:24:20vstinnerlinkissue42902 messages
2021-01-12 17:24:20vstinnercreate