TypeError: 'int' object is not subscriptable (python)

Question

I'm having problems making a matrix multiplication algorithm in python3.

This is the code:

def matrixMult(m1, m2):
    result = [[0 for x in range(len(m1))] for x in range(len(m2[0]))]
    # Iterate through rows of m1.
    for i in range(len(m1)):
        # Iterate through columns of m2.
        for j in range(len(m2[0])):
            # Iterate through rows of m2.
            for k in range(len(m2)):
                result[i][j] += m1[i][k] * m2[k][j]   # error occurs here.

    return result

Trying to call it on two random matrices like so:

m = [3, 4, 2]
n = [[13, 9, 7, 15], [8, 7, 4, 6], [6, 4, 0, 3]]
r = matrixMult(m, n)

This results in the TypeError: 'int' object is not subscriptable message.

I added a print(type()) for both the matrices declared above and they are of class 'list'. Did the same for the classes used in the function prototype, class 'list'. Hell, everything is of type 'list'. I don't know what the int object is.

Martijn Pieters · Accepted Answer · 2015-05-19 12:12:10Z

3

You are treating m1 as a nested list of integers:

result[i][j] += m1[i][k] * m2[k][j]
#               ^^^^^^^^

It is not; it is merely a simple list of integers. m1[i] then is an integer object and you cannot index integers:

>>> [3, 4, 2][0]
3
>>> [3, 4, 2][0][0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object has no attribute '__getitem__'

You probably want to use just i as the index:

result[i][j] += m1[i] * m2[k][j]

or pass in two-dimensional arrays only (so pass in [[3], [4], [2]] rather than [3, 4, 2]).

edited May 19, 2015 at 12:12

answered May 19, 2015 at 12:01

Martijn Pieters

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2 Comments

tudorv Over a year ago

Alright, thank you for the help. How would you suggest I deal with one dimensional matrices?

Martijn Pieters Over a year ago

@tudorv: well, how do you multiply a one-dimensional array with a 2-dimensional array normally? You could pass in a two-dimensional array with just one column each, or you need to adjust your multiplication code to work with one-dimensional arrays.

Cory Kramer · Accepted Answer · 2015-05-19 12:01:23Z

1

You have the following index operation

m1[i][k]

But m1 was passed in as

m = [3, 4, 2]

It only has 1 dimension to index from, not 2.

answered May 19, 2015 at 12:01

Cory Kramer

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1 Comment

tudorv Over a year ago

Alright, thank you for the help. How would you suggest I deal with one dimensional matrices?

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