input: Write a function to filter out all the vowels from a given string. If there are no vowels in the string, return the original string. This function should handle both uppercase and lowercase vowels.
  def filter_vowels(string):
       vowels = ('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U')
       return ''.join(c for c in string if c not in vowels)
  
  assert filter_vowels("hello world") == "hll wrld"
  assert filter_vowels("PYTHON") == "PYTHN"
  assert filter_vowels("AEIOUaeiou") == ""
  assert filter_vowels("") == ""
  assert filter_vowels("bcd fgh jkl") == "bcd fgh jkl"
output: def filter_vowels(string):
       vowels = ('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U')
       return ''.join(c for c in string if c not in vowels)