input: Write a function to remove all vowels from a given string. Return the string with all vowels removed.
  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 programming")=="pythn prgrmmng"
  assert filter_vowels("aeiou")==""
  assert filter_vowels("bcdfghjklmnpqrstvwxyz")=="bcdfghjklmnpqrstvwxyz"
  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)