Question

My question concerns the output of this statement:

for x in range(4), y in range(4):
    print x
    print y

Results in:

[0, 1, 2, 3]
2
True
2

It seems there is a comparison involved, I just can’t figure out why the output is structured like this.

Answer 1

My guess is that you’re running this from an interactive console, and already had y defined with a value of 2 (otherwise, you’d get NameError: name 'y' is not defined). That would lead to the output you observed.

This is due to for x in range(4), y in range(4): actually being equivalent to the following when evaluated:

for x in (range(4), y in range(4)):

which reduces to…

for x in ([0,1,2,3], 2 in range(4)):

which again reduces to…

for x in ([0,1,2,3], True):

This then results in 2 iterations of the for loop, since it iterates over each element of the tuple:

1. x = [0,1,2,3]
2. x = True.

(And of course, y is still 2.)