input: from typing import List
  
  def replace_string(input_string: str, target_string: str, replacement_string: str) -> str:
      """ Replaces all occurrences of a given string in an input string with an alternate string.
      >>> replace_string("Hello World!", "World", "Python")
      'Hello Python!'
      >>> replace_string("The cat sat on the mat", "cat", "dog")
      'The dog sat on the mat'
      >>> replace_string("My favorite food is pizza", "pizza", "sushi")
      'My favorite food is sushi'
      """
      return input_string.replace(target_string, replacement_string)
output:     return input_string.replace(target_string, replacement_string)