build regexes for matching all vowels

vowel-regex.py

#!/usr/bin/env python3

def regex_for(required_letters):
    # special cases for 1 and 2 letters, to keep things a bit tidier
    if len(required_letters) == 1:
        return required_letters[0]
    if len(required_letters) == 2:
        x,y = required_letters
        return "%s.*%s|%s.*%s" % (x,y,y,x)
    subregexes = []
    for letter in required_letters:
        remaining_letters = list(required_letters)
        remaining_letters.remove(letter)
        subregexes.append("%s.*(%s)" % (letter, regex_for(remaining_letters)))
    return '|'.join(subregexes)

print(regex_for(['a']))
print(regex_for(['a','e']))
print(regex_for(['a','e','i']))
print(regex_for(['a','e','i','o','u']))