Recursive password generator

recurpassgen.py

def get_letters(letter, choices):
    return [letter] + choices.get(letter, [])


def recurpassgen(password, passwords=[""], CHOICES={'a': ['@', '4'], 's': ['$', '&']}):
    if password == "":
        return passwords
    passwords = [p + letter for p in passwords for letter in get_letters(password[0], CHOICES)]
    return recurpassgen(password[1:], passwords=passwords)