Matrix list index out of range

Question

I've created a matrix like this:

b = [[0 for y in range(1,4)] for x in range(1,3)]

I want to have the indexes b[1:2][1:3] available, but the above code doesn't seem to do that.

range(1,4) should return numbers from 1 to 3, and range(1,3) should return numbers 1 and 2.

When i try to assign a value to b[1][3], i get an IndexError. What is the explanation of this?

`b[1][3]` is the fourth element from the second sublist, you don't have four elements `1, 2, 3 --> 3 elements`, you can only index from `0-2` — Padraic Cunningham, May 22 '16 at 23:09
Seeing what `b` actually is might help: `b = [[0, 0, 0], [0, 0, 0]]` — Moses Koledoye, May 22 '16 at 23:11

score 0 · Answer 1 · answered May 22 '16 at 23:11

range(1,4) is a list of length 3, therefore so is [0 for y in range(1,4)]. The indices available for a list are always from 0 up to the length of the list minus 1. If you want alternative indices use a dictionary.

>>> range(1, 4)
[1, 2, 3]
>>> for x in range(1, 4):
...     print(x)
...     
1
2
3
>>> L = [0 for y in range(1, 4)]
>>> L
[0, 0, 0]
>>> L[0]
0
>>> L[1]
0
>>> L[2]
0
>>> L[3]
Traceback (most recent call last):
  File "<input>", line 1, in <module>
IndexError: list index out of range

Thanks. Not sure why I thought I could make the indexing start at 1. — Jesper, May 22 '16 at 23:17

Matrix list index out of range

1 Answers1