input: def remove_vowels(string: str) -> str:
      """ Remove all vowels from a given string.
      >>> remove_vowels('hello')
      'hll'
      >>> remove_vowels('PYTHON')
      'PYTHN'
      >>> remove_vowels('Yes, we love Python!')
      'ys, w lvh Pythn!'
      """
output:     vowels = "aeiouAEIOU"
      return ''.join([char for char in string if char not in vowels])