Why does (()) equal ()?

>>> (()) == ()
True
>>&g开发者_如何学JAVAt; (())
()

() is a 0-tuple. (foo) results in the value of foo. Hence, (()) results in a 0-tuple.

From the tutorial:

; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses).

For the same reason that (4) == 4: adding parentheses around an expression does not alter its meaning (unless it would otherwise have been grouped differently of course).

Note that ( foo ) is not a 1-tuple. Otherwise things like 3 * (4 + 5) would be an error as (4 + 5) would be a 1-tuple containing 9 and you can't add a number to a 1-tuple.

I see now. From the tutorial.

; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses).

So (()) is not the tuple that contains the empty tuple - this is that tuple: ((),)