input: def filter_vowels(string: str) -> str:
      """ Filter out all the vowels from the given string.
      >>> filter_vowels('hello world')
      'hll wrld'
      >>> filter_vowels('this is a test')
      'ths s  tst'
      """
output:     vowels = "aeiouAEIOU"
      return ''.join([char for char in string if char not in vowels])