Testing equality of three values

Does this do what I think it does? It seems to me that yes. I am asking to be sure.

if n[i] == n[i+1] == n[i+2]:
    return True

Are these equal?

if n[i] == n[i+1] and n[i+1] == n[i+2]:
    return True

It is equivalent to but not equal to, since accesses are only performed once. Python chains relational operators naturally (including in and is).

The easiest way to show the slight difference:

>>> print(1) == print(2) == print(3)
1
2
3
True
>>> print(1) == print(2) and print(2) == print(3)
1
2
2
3
True

print() always returns None, so all we are doing is comparing Nones here, so the result is always True, but note that in the second case, print(2) is called twice, so we get two 2s in the output, while in the first case, the result is used for both comparisons, so it is only executed once.

If you use pure functions with no side-effects, the two operations end up exactly the same, but otherwise they are a little different.

Yes, however, when the comparisons are chained the common expression is evaluated once, when using and it's evaluated twice. In both cases the second comparison is not evaluated if the first one is false, example from 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).

As answered by others, the answer is yes. However: beware of adding parentheses. For example:

>>> 1 == 2 == 0
False
>>> (1 == 2) == 0
True

In the second case, (1 == 2) evaluates to False, and then False == 0 evaluates to True, because Python allows comparison of booleans to integers.

Likewise:

>>> 0 == 0 == 1
False
>>> (0 == 0) == 1
True

yes you are correct ....

you can also do

5 > x > 1

or

1 < x < 5

You can use set collection to test the equality

>>> a, b, c = 2, 2, 2
>>> len({a, b, c}) == 1
True
>>> a, b, c = 2, 2, 3
>>> len({a, b, c}) == 1
False

Yep, at the python's internals the comparison operators returns nor true neither false, they instead return the 'comparison result' object (cannot remember the class name, it was quite in past), and this object provides the lt, gt, eq etc etc methods and become 'responsible' for the final result (and the 'comparison result' is casting to True or False at end of statement). That's a magic of semantic control python provides to you :)

It seems that you can also chain == with !=:

>>> a = b = c = 1
>>> a == b == c
True
>>> a == b == c == 1
True
>>> a == b == c == 2
False
>>> a == b == c != 2
True
>>> a == b == c != 1
False
>>>