How and operator works in python?

Question

Could you please explain me how and works in python? I know when

x y and 0 0 0 (returns x) 0 1 0 (x) 1 0 0 (y) 1 1 1 (y)

In interpreter

>> lis = [1,2,3,4] >> 1 and 5 in lis

output gives FALSE

but,

>>> 6 and 1 in lis

output is TRUE

how does it work?

what to do in such case where in my program I have to enter if condition only when both the values are there in the list?

if i use (6 and 1 ) in lis also it is TRUE how come it is supposed to be false right? — sans0909
– sans0909, Commented Feb 9, 2016 at 9:57
I think it is 6 and (1 in lis), not (6 and 1) in lis. Otherwise 0 and 1 in [0] would evaluate to true. — khelwood
– khelwood, Commented Feb 9, 2016 at 10:02

khelwood · Accepted Answer · 2016-02-09 13:52:55Z

Despite lots of arguments to the contrary,

6 and 1 in lis

means

6 and (1 in lis)

It does not mean:

(6 and 1) in lis

The page that Maroun Maroun linked to in his comments indicates that and has a lower precedence than in.

You can test it like this:

0 and 1 in [0]

If this means (0 and 1) in [0] then it will evaluate to true, because 0 is in [0].

If it means 0 and (1 in [0]) then it will evaluate to 0, because 0 is false.

It evaluates to 0.

Even better, 0 and 0 in [0] returns 0, because and short-circuits if the first value is "not a true value".

Maroun · Accepted Answer · 2016-02-09 09:57:59Z

This lines

lis = [1,2,3,4] 1 and 5 in lis

are equivalent to

lis = [1,2,3,4] 1 and (5 in lis)

Since bool(1) is True, it's like writing

lis = [1,2,3,4] True and (5 in lis)

now since 5 is not in lis, we're getting True and False, which is False.

Community · Accepted Answer · 2017-05-23 11:59:13Z

Your statement 1 and 5 in lis is evaluated as follows:

5 in lis --> false 1 and false --> false

and 6 and 1 in lis is evaluated like this:

1 in lis --> true 6 and true --> true

The last statement evaluates to true as any number other than 0 is true

In any case, this is the wrong approach to verify if multiple values exist ina list. You could use the all operator for this post:

all(x in lis for x in [1, 5])

@Jaco, thanks for the answer could you please explain how 6 and 1 returns 1 , x(which is 6) is false and y (which is 1) is true this should return x which is false right?
@sanyesh: 6 is true! Of numbers, only 0 is false. Check it with bool(6).
I am pretty sure it is 1 and (5 in lis), not (1 and 5) in lis.

3 Answers 3