input: 
  def replace_string(input_string: str, target_string: str, replacement_string: str) -> str:
      """Replace all occurrences of the target string with the replacement string in the input string.
      >>> replace_string("Hello World!", "World", "Python")
      'Hello Python!'
      >>> replace_string("Hello World! Hello World!", "World", "Python")
      'Hello Python! Hello Python!'
      """
      return input_string.replace(target_string, replacement_string)
  
output:     return input_string.replace(target_string, replacement_string)