Question

This doesn’t make sense to me yet. So the first while loop runs and prints matrix[0][0], matrix[0][1], matrix[0][2] and matrix[0][3] until j=4 and isn’t less than len(matrix[i]). Okay, but now it pops out and goes back up to while i<len(matrix):. Wouldn’t this make it read j=0 again and go straight back into the nested while loop?

matrix = [[4,5,6,7],[2,4,9,3]]
i=0
while i<len(matrix):
    j=0
    while j<len(matrix[i]):
        print matrix[i][j]
        j=j+1
    i=i+1

Answer 1

Yes, and that’s exactly what it does.

See for yourself by adding a print statement:

matrix = [[4,5,6,7],[2,4,9,3]]
i=0
while i<len(matrix):
    j=0
    while j<len(matrix[i]):
        print 'i = {}, j = {}, element = {}'.format(i,j,matrix[i][j])
        print matrix[i][j]
        j=j+1
    i=i+1

---

By the way, that is a very unpythonic way to loop in python. This is equivalent, and more suited to the language:

matrix = [[4,5,6,7],[2,4,9,3]]
for row in matrix:
  for element in row:
    print element