Bug With Logic Operator "or"?

I'm learning the language python. And although it is very simple indeed, I got some unexpected results using logic operators both in IDLE and in python. I made a simple test in IDL

Solution 1:

OR returns the first TRUE value it encounters.

That is:

>>> (2 or 10) 
# returns 2
>>> (10 or 2)
# returns 10

Update

To address OP's comment below:

There are truthy values which evaluate to True and there are falsey values which evaluate to False. For example, 0 is a falsey value. Rest of the integers are truthy values. Therefore, 10 is also a truthy value.

If you do:

>>> if 10: # since 10 is truthy, this statement will execute.
        print("Okay!")
    else:
        print("Not okay!")

# prints "Okay!"

Moving on, 10 or 2 in range(1, 6) evaluates to 10 or (2 in range(1, 6)).

 10     or     (2 in range(1, 6))
\__/           \________________/
True               True

# Returns 10 because it's a truthy value. 
# OR operator only evaluates until it finds a True value.

Let's see another example:

 0      or    10
\_/          \__/
False        True

# Returns 10 because 0 is a falsey value, so the 
# OR operator continues evaluating the rest of the expression

Finally, let's see the if expression:

 >>> if 10 or 2 in range(1, 6):
        print("True")
     else:
        print("False")
 # prints "True"

It prints True because 10 or 2 in range(1, 6) returns 10 and as we saw above, if 10 evaluates to True, hence, the if block is executed.

---

Additionally:

The correct expression will be this:

>>> 10 in range(1, 6) or 2 in range(1, 6)
# returns True

This expression will return True because even though 10 is not in the given range, but 2 is.

10 in range(1, 6)   or   2 in range(1, 6)
\_______________/        \______________/ 
     False                     True

# Returns True because OR will keep on evaluating
# until it finds a True value

But if you want to check if 10 and 2 both are in the range, you'll have to use the AND operator:

>>> 10 in range(1, 6) and 2 in range(1, 6)
# returns False