input: Write a function to filter out all the vowels from a given string. If the given string is empty then return an empty string.
  
  assert filter_vowels("hello")=="hll"
  assert filter_vowels("world")=="wrld"
  assert filter_vowels("aeiouAEIOU")==""
  assert filter_vowels("")==""
  assert filter_vowels("Python")=="Pythn"
output: def filter_vowels(s):
      vowels = "aeiouAEIOU"
      return ''.join([char for char in s if char not in vowels])