Generate alphanumeric strings sequentially

Question

I\'m trying to create a loop to generate and print strings as follows:

1. Alphanumeric characters only:
2. 0-9 are before A-Z, which are before a-z,

Answer 1

from string import digits, ascii_uppercase, ascii_lowercase
from itertools import product
chars = digits + ascii_uppercase + ascii_lowercase

def give_me_next(lst):
        lst = lst[::-1]
        change_next = False
        change = True
        n = 0
        for x in lst:
                if change_next == True:
                        change_next = False
                        pos = chars.find(x)
                        try:
                                a =  chars[pos+1]
                                lst = list(lst)
                                lst[n] = a
                                lst = "".join(lst)
                                x = a
                        except:
                                lst = list(lst)
                                lst[n] = '0'
                                lst = "".join(lst)
                                change_next = True
                                x = '0'

                pos = chars.find(x)
                try:
                        a =  chars[pos+1]
                        if change == True:
                                lst = list(lst)
                                lst[n] = a
                                lst = "".join(lst)
                                change = False
                except:
                        lst = list(lst)
                        lst[n] = '0'
                        lst = "".join(lst)
                        change_next = True

                n = n + 1

        lst = lst[::-1]
        return lst

a=  give_me_next('zzzzz')
while True:
        a =  give_me_next(a)
        print a