input: Write a function to remove all vowels from a given string. If the given string is empty, return an empty 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("")==""
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