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