input: from typing import List, Tuple
  
  def replace_string(input_string: str, target_string: str, replacement_string: str) -> str:
      """ Replaces all occurrences of a given string within an input string 
      with an alternate string.
      
      >>> replace_string("Hello World!", "World", "Python")
      'Hello Python!'
      >>> replace_string("Hello World! How are you, World?", "World", "Universe")
      'Hello Universe! How are you, Universe?'
      """
      return input_string.replace(target_string, replacement_string)
output:     return input_string.replace(target_string, replacement_string)