input: 
  def filter_vowels(string):
      """Filter out all the vowels from a given string.
      >>> filter_vowels('hello world')
      'hll wrld'
      >>> filter_vowels('python')
      'pythn'
      """
  
output:     vowels = "aeiouAEIOU"
      result = ""
      for char in string:
          if char not in vowels:
              result += char
      return result