input: Write a function to filter out all the vowels from a given string. If the given 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")=="hll"
  assert filter_vowels("world")=="wrld"
  assert filter_vowels("aeiou")==""
  assert filter_vowels("bcdfgh")=="bcdfgh"
  assert filter_vowels("")==""
output: def filter_vowels(string):
       vowels = ('a', 'e', 'i', 'o', 'u')
       return ''.join(c for c in string if c not in vowels)