ParserBase could be optimized

There is a lot of wasteful CPU code in this fashion (seen multiple times) :-

if ")" in rawdata[j:]:
    j = rawdata.find(")", j) + 1

search performed in string twice, even if we could just do it once.
Consider the strings immutable, then on every slice a new string is created on the fly.
Moreover, the slicing done at rawdata[j:], is bound to be quite expensive depending on the size of the string.
We could eliminate slicing altogether and only have one find operation in this style :-

RPAREN_pos = rawdata.find(")", j)
if find_RPAREN != -1:
    j = RPAREN_pos + 1

I'm new to Open Source Code Contributions. Would love to learn from other's coding style & know other's point of view.

Originally posted by @be-thomas in https://github.com/python/cpython/issues/92084#issuecomment-1114023102