Odd behaviour: What does "12 in [12,13,14] == True" mean in Python

Question

I would have expected it to either have parenthesis to the left or to the right.

But it seems to do something else!

>>> 12 in [12,13,14] == True
False
>>> (12 in [12,13,13]) == True
True
>>> 12 in ([12,13,14] == True)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: argument of type 'bool' is not iterable

Answer 1

That the following expression evaluates to False may be surprising:

12 in [12,13,14] == True

Here's what's happening: the in and == operators have the same precedence, and they support left-to-right chaining (see the docs), so the expression is equivalent to

12 in [12,13,14] and [12,13,14] == True

Now and is less binding, and the left-hand side obviously evaluates to True. Now for the tricky part: a non-empty sequence, such as the [12, 13, 14] list evaluates to True, but it is not equal to True. It's a so-called "truthy" value. Truthy and Falsy values are not booleans (not instances of type bool), but they evaluate to either True or False.

So they right-hand side of the and comparison evaluates to False.