Python nested range function

Question

What is the output of the following nested control structure in Python when executed?

for x in range(3):
    for y in range(x):
        print x,y

I know the answer is

1 0
2 0
2 1

But it is not clear for me why it is this output.
I know that the range(3) function would give you {0, 1, 2} so why is not the first output 0 0 instead of 1 0?

Answer 1

Because range(0) returns an empty list [], so the inner loop does nothing the first time it is run.