input: def filter_vowels(string: str) -> str:
      """Filter out all the vowels from the given string.
      >>> filter_vowels("hello")
      "hll"
      >>> filter_vowels("aardvark")
      "rdvrk"
      """
output:     vowels = "aeiouAEIOU"
      return ''.join([char for char in string if char not in vowels])