2 dimensional loop doesn't work as expected in python

Question

I have this loop:

i = 0
j = 1
size = 4

for i in range(i, i + size):
    for j in range(j, j + size):
        print(i, j)

I expected it to have the following output:

0 1
0 2
0 3
0 4
1 1
1 2
. .
. .
. .
3 4

But I get this instead:

0 1 
0 2 
0 3 
0 4 
1 4 
1 5 
1 6 
1 7 
2 7 
2 8 
2 9 
2 10
3 10
3 11
3 12
3 13

It's like the value of j is being updated after each outer loop iteration. Why is this happening?

Answer 1

You are setting variable initially and using variables with the same name in the loop... use variable with different names in the loop like a and b :

i = 0
j = 1
size = 4

for a in range(i, i + size):
    for b in range(j, j + size):
        print(a, b)

0 1
0 2
0 3
0 4
1 1
1 2
1 3
1 4
2 1
2 2
2 3
2 4
3 1
3 2
3 3
3 4

Answer 2

It's like the value of j is being updated after each outer loop iteration. Why is this happening?

This is because you set the value of j with for j in range(j, j + size) . In other words, j is set to a new value each time the inner loop iterates. Similarly, you set i to a new value each time the outer loop iterates just like you see in the output.