Precedence of `in` and `==` in Python

Question

Suppose I have the following line of code:

print("valley" in "hillside" == False)

Since the precedence of in and == is equivalent in Python, I expected the operations to be performed from left to right, producing True as the output.

However, in actuality, when I run this line of code, I get False.

I have noticed that adding brackets around "valley" in "hillside" results in True as the output but I don't seem to understand why it's necessary in the first place...

Not really. According to the documentation, `==` and `in` have the same precedence. — nugget_boi, Mar 28 '20 at 12:25
Yes, but the documentation also describes the chaining in quite some detail. — Kelly Bundy, Mar 28 '20 at 12:25

score 3 · Accepted Answer · answered Mar 28 '20 at 12:27

Both in and == are comparison operators, so the parser treats

print("valley" in "hillside" == False)

the same as

print("valley" in "hillside" and "hillside" == False)

See the section on Comparisons in the Python language reference for more details, in particular this note:

Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).

That makes sense- Thanks! – nugget_boi Mar 28 '20 at 12:30 — nugget_boi, Mar 28 '20 at 12:30

Precedence of `in` and `==` in Python

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