input: Write a function to filter out all the vowels from a given string. If the string is empty, return an empty string.
  def filter_vowels(string):
      vowels = ('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("aeiou") == ""
  assert filter_vowels("") == ""
  assert filter_vowels("This is a test") == "Ths s  tst"
output: def filter_vowels(string):
      vowels = ('a', 'e', 'i', 'o', 'u')
      return ''.join(c for c in string if c.lower() not in vowels)