input: Write a function to remove all vowels from a given string and return the modified string. Vowels include 'a', 'e', 'i', 'o', 'u' (both uppercase and lowercase).
  
  def remove_vowels(string):
      vowels = ['a','e','i','o','u']
      new_string = ''
      for char in string:
          if char.lower() not in vowels:
              new_string += char
      return new_string
  
  assert remove_vowels("Hello World!") == "Hll Wrld!"
  assert remove_vowels("Python Programming") == "Pythn Prgrmmng"
  assert remove_vowels("AI is amazing") == " s mzng"
  assert remove_vowels("aeiouAEIOU") == ""
  assert remove_vowels("") == ""
output: def remove_vowels(string):
      vowels = ['a','e','i','o','u']
      new_string = ''
      for char in string:
          if char.lower() not in vowels:
              new_string += char
      return new_string