input: from typing import List
  
  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("Python is fun!", "Python", "Java")
      "Java is fun!"
      """
      return input_string.replace(target_string, replacement_string)
  
  print(replace_string("Hello World!", "World", "Python"))
output:     return input_string.replace(target_string, replacement_string)