input: Write a function to remove all vowels from a given string. Define the function as `filter_vowels` which takes a string as input and returns a new string with all vowels removed.
  assert filter_vowels("hello")=="hll"
  assert filter_vowels("this is a test")=="ths s  tst"
  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])