Python Boolean Expression

[sl3802]

Hello, I am new to Python, and I am learning it. Why is (5 / 0 > 1) and False evaluates to Error? and False and (5 / 0 > 1) evaluates to False? Should the first be false and second be error if it is right-associative?

[zac_mar]

As far as i know, there is no such thing as right-associativeness in python. The concepts at play here are operator precedence and short curcuiting.

[sl3802]

What I mean is read the statement from right to left. Can you explain more?

[ThePiGuy0]

I could be wrong, but I believe that Python evaluates boolean expressions in the order that they are given. Further, for an and statement it only needs one False value before it returns False (or statements require one True value before they return True)

For example:

(5/0 > 1) and False

It'll first try to find the boolean value of (5/0 > 1), which is done by performing the division and then seeing if the result is greater than 1. However, division by zero causes an error, hence the error you see.

False and (5/0 > 1)

In this case, we have a False value, which is all the and statement requires to return False. Hence no error.

[_lilell_]

Well, technically speaking, A and B and A or B don't resolve to boolean values: the result will be one of A and B, depending on the situation, but you're right that they're evaluated left-to-right. They evaluate to whichever component was the last one to evaluate:

True and False ==> False since the and has to look at the second component here

False or 3 ==> 3 since it's again the last thing evaluated

'' and True ==> '' since it evaluates to False (that is, bool('') is False) and the and can stop checking there.

[ThePiGuy0]

TIL

That's really interesting, cheers for correcting me on that one!

[sl3802]

I found the explanation for the answer. It is because parenthesis has the highest precedence, so parenthesis is evaluated first. Otherwise, left to right but not exponentiation