Python3: multiple operators with same precedence

Question

I recently started to learn Python.

And my friend asked me which value 3 < 5 != True evaluates to.

As I have prior experience to javascript and c++, I answered False. (I was able to see false in both languages)

Because, operators with same precedence (comparison) works left to right.

So that 3 < 5 is evaluated first, which becomes True and True != True is False.

I believed it was right answer.

But it turned out it wasn't.

I ran this expression on my computer and it said it's True.

Am I missing something? or Python evaluates operators with same precedence in different way?

jpp · Accepted Answer · 2018-09-30T23:59:06.047

7

The expression 3 < 5 != True is evaluated as:

(3 < 5) and (5 != True)

Since True == 1, this equates to:

(3 < 5) and (5 != 1)

Of course, both parts evaluate to True and therefore your result is True.

Chained comparisons are described in the docs:

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).

edited Sep 30 '18 at 23:59

answered Sep 30 '18 at 23:56

jpp

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Nice answer, but maybe explain a bit more how `3 < 5 != True` equals `(3 < 5) and (5 != True)`. – Christian Dean Sep 30 '18 at 23:57
2

@ChristianDean, I don't think I can explain it better than the docs, so I've included a quote. – jpp Sep 30 '18 at 23:59
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Yeah, fair point @jpp – Christian Dean Oct 01 '18 at 00:00
I think it's intended to work the same way as conventional mathmatical expression where a < b < c means (a < b) and (b < c) unlike other programming languages – Gompro Oct 01 '18 at 00:03

Python3: multiple operators with same precedence

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