import string

a = string.ascii_lowercase        # a = 'abcdefghijklmnopqrstuvwxyz'
b = string.ascii_uppercase        # b = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
c = string.ascii_letters          # c = a + b
d = string.digits                 # d = '0123456789'
x = string.hexdigits              # x = '0123456789abcdefABCDEF'

