[issue37348] Optimize PyUnicode_GetString for short ASCII strings

[STINNER Victor]

STINNER Victor <vstinner at redhat.com> added the comment:

> _PyUnicode_FromASCII(s, len) is faster than PyUnicode_FromString(s) because PyUnicode_FromString() uses temporary _PyUnicodeWriter to support UTF-8.

I don't understand how _PyUnicodeWriter could be slow. It does not overallocate by default. It's just wrapper to implement efficient memory management.

> Oh, wait.  Why we used _PyUnicodeWriter here?

To optimize decoding errors: the error handler can use replacement string longer than 1 character. Overallocation is used in this case.

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