Why in Python does “0, 0 == (0, 0)” equal “(0, False)”?

Question

In Python (I checked only with Python 3.6 but I believe it should hold for many of the previous versions as well):

(0, 0) == 0, 0   # results in a two elemen         


        

Answer 1

Another way to explain the problem: You're probably familiar with dictionary literals

{ "a": 1, "b": 2, "c": 3 }

and array literals

[ "a", "b", "c" ]

and tuple literals

( 1, 2, 3 )

but what you don't realize is that, unlike dictionary and array literals, the parentheses you usually see around a tuple literal are not part of the literal syntax. The literal syntax for tuples is just a sequence of expressions separated by commas:

1, 2, 3

(an "exprlist" in the language of the formal grammar for Python).

Now, what do you expect the array literal

[ 0, 0 == (0, 0) ]

to evaluate to? That probably looks a lot more like it should be the same as

[ 0, (0 == (0, 0)) ]

which of course evaluates to [0, False]. Similarly, with an explicitly parenthesized tuple literal

( 0, 0 == (0, 0) )

it's not surprising to get (0, False). But the parentheses are optional;

0, 0 == (0, 0)

is the same thing. And that's why you get (0, False).

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If you're wondering why the parentheses around a tuple literal are optional, it is largely because it would be annoying to have to write destructuring assignments that way:

(a, b) = (c, d) # meh
a, b = c, d     # better