input: def filter_vowels(string: str) -> str:
      """Filter out all vowels from a given string.
      
      >>> filter_vowels('hello world')
      'hll wrld'
      >>> filter_vowels('Python Programming')
      'Pythn Prgrmmng'
      """
output:     vowels = "aeiouAEIOU"
      return ''.join([char for char in string if char not in vowels])