In normalizestring(),
            ch = Py_TOLOWER(Py_CHARMASK(ch));
Where Py_TOLOWER is defined as following,
            #define Py_TOLOWER(c) (_Py_ctype_tolower[Py_CHARMASK(c)])

Redundant Py_CHARMASK called here.

Good catch ;), try to fix it, thanks.

Looks the PR is confused. Make sure: one PR on one dev branch.

Thanks Hai, for your careful check. There is a misoperation in PR 15093. Now I closed PR 15093. And resubmit code as PR 15095.

Search "Py_CHARMASK" in Python source code, there are more than a dozen Py_CHARMASK can be deleted:

https://github.com/python/cpython/blob/e42b705188271da108de42b55d9344642170aa2b/Python/mystrtoul.c#L102

https://github.com/python/cpython/blob/e42b705188271da108de42b55d9344642170aa2b/Python/dynload_aix.c#L143

https://github.com/python/cpython/blob/530f506ac91338b55cf2be71b1cdf50cb077512f/Modules/unicodedata.c#L963

...

Or remove Py_CHARMASK in Py_ISxxx/Py_TOLOWER/Py_TOUPPER macros?
Sometimes `c` is already a unsinged char, Py_CHARMASK is not necessary in these cases.

Thanks Ma,I also think all these redundant Py_CHARMASK should be deleted.

After the full search for the project code, there are more than a dozen similar issues that need to be modified. A new PR will be added later.

VC2017 optimizes multiple `unsigned char)((c) & 0xff` to a single `movzx` operation, maybe other compilers do it as well.
If so, there will be no performance changes.

Hi Ma, 
    I think this is a very valuable suggestion.
    And if we want to delete the definition of Py_CHARMASK, maybe another issue needed.
    I am not very sure about the considerations of this macro definition. And whether there are any side effects after deletion needs further discussion.

Thanks,
Best Regards

Due to this macro documented in https://docs.python.org/3.9/c-api/intro.html#c.Py_CHARMASK and we don't know how much user use this marco, I don't think we need delte this function(deleting operation should be careful).

typo error: delte->delete

New changeset 2ec70102066fe5534f1a62e8f496d2005e1697db by Steve Dower (Jordon Xu) in branch 'master':
bpo-37752: Delete redundant Py_CHARMASK in normalizestring() (GH-15095)
https://github.com/python/cpython/commit/2ec70102066fe5534f1a62e8f496d2005e1697db

Thanks for the patch!