How To Implement Addition To All Submatrix Elements?

I'm trying to implement matrix class for simple operations with plain python (no numpy and etc.). Here is part of it: class Matrix(list): def __getitem__(self, item): t

Solution 1:

First, inheriting from list is a bad move here. A matrix doesn't support the kinds of operations a list does; for example, you can't append to or extend a matrix, and item assignment is completely different. Your matrix should contain a list, not be a list.

As for what magic methods you need, m[0:2, 0:2] += 1 roughly translates to the following:

temp = m.__getitem__((slice(0, 2), slice(0, 2)))
temp = operator.iadd(temp, 1)
m.__setitem__((slice(0, 2), slice(0, 2)), temp)

where operator.iadd tries temp.__iadd__, temp.__add__, and (1).__radd__ to perform the addition.

You need to implement __getitem__ and __setitem__ to retrieve the submatrix and assign the new submatrix. Additionally, __getitem__ will need to return a matrix, rather than a list.

You should probably implement both __add__ and __iadd__; while __add__ alone would be sufficient for this case, __iadd__ will be necessary for operations like m += 1 to work in-place instead of replacing m with a new matrix object.

Solution 2:

NO. __iadd__ will do the trick for you if the magic was:

m += 2

But the magic is executed over m[0:2, 0:2]. You need to ensure that when slicing your matrix you get a different object, and not a list of lists, since list of lists do not support __iadd__.