[FIXED] Strange Python boolean operator

Issue

I saw some variations of the following simple piece of code:

if dist_1>dist_2 :
    print enemy_2
else:
    print enemy_1

Variation 1:

print (enemy_1, enemy_2)[dist_1 > dist_2]

Variation 2:

e1, d1, e2 = (raw_input() for _ in '123')
print (e1, e2)[d1 > raw_input()]

Can someone please explain how this print (x,y)[x>y] code works?

Solution

Booleans are actually a subclass of integers in Python:

isinstance(True, int)
isinstance(False, int)

are both true statements. So you can index a two-element sequence with a boolean. If the boolean is False, you will get the first element. If the boolean is True, you will get the second element.

The expression (enemy_1, enemy_2) creates a two-element tuple. [dist_1 > dist_2] provides the boolean index. The print is incidental; it is just used to output the result.

Answered By - Mad Physicist