input: def explain_difference(data_type: str) -> str:
      """
      Explain the difference between a list and a tuple in Python.
      >>> explain_difference('list')
      'A list is mutable, meaning its contents can be changed. It has square brackets around it.'
      >>> explain_difference('tuple')
      'A tuple is immutable, meaning its contents cannot be changed. It has parentheses around it.'
      """
      if data_type == 'list':
          return 'A list is mutable, meaning its contents can be changed. It has square brackets around it.'
      elif data_type == 'tuple':
          return 'A tuple is immutable, meaning its contents cannot be changed. It has parentheses around it.'
      else:
          return 'Invalid data type.'
output:     else:
          return 'Invalid data type.'