increment a string (i.e. "A" => "B", "Z" => "AA", "AA" => "AB", etc.) in Python (in Perl, assuming "A" is in $s, it's $s++)

increment.py

# lifted from http://bit.ly/2iJfRou (codereview.stackexchange.com)
# yeah, I can't believe how painful this is in Python.  Perl's auto-incrementing
# strings have this beat by a mile.
def incr_chr(c):
    return chr(ord(c) + 1) if c != 'Z' else 'A'

def incr_str(s):
    lpart = s.rstrip('Z')
    num_replacements = len(s) - len(lpart)
    new_s = lpart[:-1] + incr_chr(lpart[-1]) if lpart else 'A'
    new_s += 'A' * num_replacements
    return new_s