input: Write a function to filter out all the vowels from a given string. The function should return the string with all vowels removed. If the input string is empty, the function should return an empty string.
  assert filter_vowels('hello world')=='hll wrld'
  assert filter_vowels('aeiou')==''
  assert filter_vowels('python')=='pythn'
  assert filter_vowels('')==''
  assert filter_vowels('This is a test')=='Ths s  tst'
output: def filter_vowels(s):
      vowels = "aeiouAEIOU"
      return ''.join([char for char in s if char not in vowels])