input: Write a function to remove all vowels from a given string.
  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("AEIOUaeiou") == ""
  assert remove_vowels("12345") == "12345"
  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