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

'A*' means match any number of A's. Even 0.

Here's how to match a string with an even number of a's, upper or lower:

re.compile(r'''
    ^
    [^a]*
    (
        (
            a[^a]*
        ){2}
    # if there must be at least 2 (not just 0), change the
    # '*' on the following line to '+'
    )* 
    $
    ''',re.IGNORECASE|re.VERBOSE)

You probably are using a as an example. If you want to match a specific character other than a, replace a with %s and then insert

[...]
$
'''%( other_char, other_char, other_char )
[...]