import string

a = string.lowercase        # a = 'abcdefghijklmnopqrstuvwxyz'
b = string.uppercase        # b = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
c = string.letters          # c = a + b
d = string.digits           # d = '0123456789'
x = string.hexdigits        # x = '0123456789abcdefABCDEF'

