Regex match even number of letters

Question

I need to match an expression in Python with regular expressions that only matches even number of letter occurrences. For example:

AAA        # no match
AA         # match
fsfaAAasdf # match
sAfA       # match
sdAAewAsA  # match
AeAiA      # no match

An even number of As SHOULD match.

Answer 1

Try this regular expression:

^[^A]*((AA)+[^A]*)*$

And if the As don’t need to be consecutive:

^[^A]*(A[^A]*A[^A]*)*$