Bug report

3.11.0b1 appears to have a regression in the behavior ofPy_InitializeFromConfig() in the way thatsys.path is computed.

Reproduction case 1:

This code attempts to set the path through theconfig.pythonpath_env variable.

int main(int argc, char *argv[]) {    PyConfig config;    PyConfig_InitIsolatedConfig(&config);    PyConfig_SetString(&config, &config.pythonpath_env, L"/path/to/app:/other/path");    Py_InitializeFromConfig(&config);       PyRun_SimpleString("import sys; print(f'{sys.path=}')");    return 0}

In Python 3.8.13, 3.9.12 and 3.10.4, this code shows 6 items when sys.path is printed:

• /path/to/app
• /other/path
• /path/to/Python/lib/python3X.zip
• /path/to/Python/lib/python3.X
• /path/to/Python/lib/python3.X/lib-dynload
• /path/to/Python/lib/python3.X/site-packages

In Python 3.11.0b1, the first two items are not present.

Reproduction case 2:

This example is a closer match to the"more complete example" in the docs; it reads a full configuration, then appending the extra search paths.

int main(int argc, char *argv[]) {    PyConfig config;    PyConfig_InitIsolatedConfig(&config);    PyConfig_Read(&config);    PyWideStringList_Append(&config.module_search_paths, L"/path/to/app");    PyWideStringList_Append(&config.module_search_paths, L"/other/path");    Py_InitializeFromConfig(&config);       PyRun_SimpleString("import sys; print(f'{sys.path=}')");    return 0}

Again, in Python 3.8.13, 3.9.12 and 3.10.4, this code shows 6 items when sys.path is printed (although the order is different):

• /path/to/Python/lib/python3X.zip
• /path/to/Python/lib/python3.X
• /path/to/Python/lib/python3.X/lib-dynload
• /path/to/app
• /other/path
• /path/to/Python/lib/python3.X/site-packages

In Python 3.11.0b1, this raises an error, dumping the path configuration with_Py_DumpPathConfig(). This appears to be because it's modifying the path enough to make theencodings module unimportable.

If the 2 path appends are omitted (but thePyConfig_Read() call is retained), it runs, and outputs sys.path - but with the 2 custom module search paths missing.

Analysis

As best as I can make out, the regression was introduced by99fcf15 (cc@zooba) as part of a refactor ofgetpath().

Your environment

Observed in Python 3.11.0b1 on macOS 12.3.1 on M1 hardware; however, I don't think there's anything Mac specific about it.

FWIW, I discovered this while porting thesupport library used byBriefcase to publish macOS and iOS apps.