_PySys_InitCore() and _PySys_InitMain() in Python/sysmodule.c contains many invocations of macros for setting attributes of the sys module. The proposed PR changes these macros.

1. SET_SYS_FROM_STRING was renamed to just SET_SYS. It is much shorter and allow to write many invocations in one line. Also SET_SYS_FROM_STRING was not consistent with SET_SYS_FROM_WSTR.

2. Added new SET_SYS_FROM_STRING which sets attribute specified as C char string (similarly to SET_SYS_FROM_WSTR which sets attribute specified as C wchar_t string).

3. Added COPY_SYS_ATTR for making a copy of the attribute. It uses PyMapping_GetItemString() instead of PyDict_GetItemString() which silences all expressions.

4. Removed SET_SYS_FROM_STRING_BORROW. It no longer used, and it was used improperly.

5. SET_SYS_FROM_STRING_INT_RESULT replaced with SET_SYS.

6. All macros have been rewritten in term of SET_SYS that significantly simplifies the code.

All this makes the code clearer and makes errors handling more correct.

New changeset fa1d83db62a545580d9a1a585b2c1fb55961a5c3 by Serhiy Storchaka in branch 'master':
bpo-42002: Clean up initialization of the sys module. (GH-22642)
https://github.com/python/cpython/commit/fa1d83db62a545580d9a1a585b2c1fb55961a5c3