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