Python

<code>def add_lists(a, b):
    """
      >>> add_lists([1, 1], [1, 1])
      [2, 2]
      >>> add_lists([1, 2], [1, 4])
      [2, 6]
      >>> add_lists([1, 2, 1], [1, 4, 3])
      [2, 6, 4]
    """
    new_list = []
    i = 0
    while i < len(a):
        new_list += a(i) + b(i)
        i += 1
    return new_list

if __name__ == '__main__':
    import doctest
    doctest.testmod()</code>

TypeError: 'list' object is not callable

How can I fix this?

>>17
It means that the code will only be executed if you run that file directly (i.e. as "__main__"), but won't run if you use that file as a library. It's useful for tests.