input: from typing import Tuple
  
  
  def replace_string(input_string: str, target_string: str, replacement_string: str) -> str:
      """Replace all occurrences of a given string with an alternate string.
      >>> replace_string("Hello World!", "World", "Python")
      'Hello Python!'
      >>> replace_string("Hello World!", "o", "a")
      'Hella Warld!'
      """
      return input_string.replace(target_string, replacement_string)
output:     return input_string.replace(target_string, replacement_string)