input: Write a function to filter out all the vowels from a given string and return the modified string.
  assert filter_vowels("hello")=="hll"
  assert filter_vowels("python")=="pythn"
  assert filter_vowels("aeiou")==""
  assert filter_vowels("")==""
  assert filter_vowels("bcdfgh")=="bcdfgh"
output: def filter_vowels(s):
      vowels = "aeiouAEIOU"
      return ''.join([char for char in s if char not in vowels])