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                


        

Answer 1

Try this regular expression:

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

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

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