How to tell if chr returns a valid character python code example

Example 1: all characters python

'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

Example 2: python check if character is letter

>>> 'A'.isalpha()
True
>>> '1'.isalpha()
False