Python: Generate String Combinations with set count of type. (String of x length with, x numbers, x uppercase, x lowercase)

Question

Looking for most efficient way to generate string combinations with qualifiers,

A string of length 16, with 2 numbers, 8 lowercase, 6 uppercase, a way to iterate over all combinations.

Perhaps using itertools.filterfalse or itertools.dropwhile?

Answer 1

Here is a possible solution:

from itertools import combinations_with_replacement, permutations, product
from string import ascii_digits, ascii_lowercase, ascii_uppercase
from sympy.utilities.iterables import multiset_permutations

def generator():
    n_gen = combinations_with_replacement(ascii_digits, 2)
    l_gen = combinations_with_replacement(ascii_lowercase, 8)
    u_gen = combinations_with_replacement(ascii_uppercase, 6)
    for numbers, lowercase, uppercase in product(n_gen, l_gen, u_gen):
        for p in multiset_permutations(numbers + lowercase + uppercase):
            yield ''.join(p)

Example (print 100 strings):

g = generator()
i = 0

for s in g:
    if i > 100:
        break
    print(s)
    i += 1

Of course you should not print them all, there are too many!! Indeed there are more than 10^26 possible strings! Do NOT create a list with them unless you know what you are doing.