Counting using a generator which returns the digits of an arbitrary number system

count.py

def count(digitgen):
    "Takes an iterator which yields the digits of a number system and counts using it."
    
    def subcount(digitgen, places):
        if places == 1:
            for d in digitgen():
                yield d
        else:
            for d in digitgen():
                for ld in subcount(digitgen, places - 1):
                    yield d + ld
                    
    for d in digitgen():
        yield d
    
    places = 2
    while True:
        first = True
        for d in digitgen():
            if first:
                first = False
                continue
            for ld in subcount(digitgen, places - 1):
                yield d + ld
        places += 1

if __name__ == "__main__":
    import string
    def labelelements():
        for char in string.ascii_lowercase:
            yield char
        for char in string.ascii_uppercase:
            yield char
    
    def base2():
        for d in range(2):
            yield str(d)

    i = 0
    for label in count(labelelements):
        print i, ":", label
        i += 1
        if i > 200:
            break;
    i = 0
    for b2 in count(base2):
        print i, ':', b2
        i += 1
        if i > 200:
            break