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