How to to read a matrix from a given file?

You can do this:

fin = open('input.txt','r')
a=[]
for line in fin.readlines():
    a.append( [ int (x) for x in line.split(',') ] )

You can simply use numpy.loadtxt. Easy to use, and you can also specify your delimiter, datatypes etc.

specifically, all you need to do is this:

import numpy as np
input = np.loadtxt("input.txt", dtype='i', delimiter=',')
print(input)

And the output would be:

[[0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 2 1 0 2 0 0 0 0]
 [0 0 2 1 1 2 2 0 0 1]
 [0 0 1 2 2 1 1 0 0 2]
 [1 0 1 1 1 2 1 0 2 1]]

Consider

with open('input.txt', 'r') as f:
    l = [[int(num) for num in line.split(',')] for line in f]
print(l)

produces

[[0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 2, 1, 0, 2, 0, 0, 0, 0], [0, 0, 2, 1, 1, 2, 2, 0, 0, 1], [0, 0, 1, 2, 2, 1, 1, 0, 0, 2], [1, 0, 1, 1, 1, 2, 1, 0, 2, 1]]

Note that you have to split on commas.

---

If you do have blank lines then change

l = [[int(num) for num in line.split(',')] for line in f ]

to

l = [[int(num) for num in line.split(',')] for line in f if line.strip() != "" ]