input: def filter_vowels(string: str) -> str:
      """Given a string, filter out all the vowels and return the modified string.
      >>> filter_vowels("hello world")
      'hll wrld'
      >>> filter_vowels("aeiou")
      ''
      """
output:     vowels = "aeiouAEIOU"
      return ''.join([char for char in string if char not in vowels])