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 with an alternate string.
      >>> replace_string("Hello World!", "World", "Python")
      'Hello Python!'
      >>> replace_string("Python is fun and Python is great", "Python", "Java")
      'Java is fun and Java is great'
      """
      return input_string.replace(target_string, replacement_string)
output:     return input_string.replace(target_string, replacement_string)