input: Write a python function to get vowels from a string.
  assert get_vowels('hello world') == ['e', 'o', 'o']
  assert get_vowels('python programming') == ['o', 'o', 'a', 'i']
  assert get_vowels('bcdfghjklmnpqrstvwxyz') == []
  assert get_vowels('AEIOUaeiou') == ['a', 'e', 'i', 'o', 'u', 'a', 'e', 'i', 'o', 'u']
output: def get_vowels(s):
      vowels = "aeiouAEIOU"
      return [char for char in s if char in vowels]