If the first character is an integer, it will not capitalize the first letter.
>>> '2s'.capitalize() '2s'
If you want the functionality, strip off the digits, you can use
'2'.isdigit() to check for each character.
>>> s = '123sa' >>> for i, c in enumerate(s): ... if not c.isdigit(): ... break ... >>> s[:i] + s[i:].capitalize() '123Sa'