错误：“矩阵”object 不可下标

Question

I have created a class in python for matrices and want to have different functions that when applied to a matrix object accomplishes a specific goal. The specific function which have an error is a function to add one matrix to another.

class Matrix:
  def __init__(self, rows):
    self.rows = rows    
    self.m = len(rows) 
    self.n = len(rows[0])


  def add(self,other):
     output = [[0 for x in range(self.m)] for y in range(self.m)]
     for i in range(self.m):
       for j in range(self.n): 
         output[i][j] = self[i][j] + other[i][j]
     returnmatrix = Matrix(output)
     return returnmatrix

B = Matrix([[1,2,3], [4,5,6], [7,8,9]])
F = Matrix([[1,2,3], [4,5,6], [7,8,9]])
B.add(F)

I expect the output to be a 3x3 matrix that is the addition of matrices B and F. Error recieved is: TypeError: 'Matrix' object is not subscriptable.

Answer 1

The error comes from this line;

for j in range(self.n): 
    output[i][j] = self[i][j] + other[i][j]

You are subscripting the object but presumably need to be subscripting the rows attribute:

for j in range(self.n): 
    output.rows[i][j] = self.rows[i][j] + other.rows[i][j]

Also for this to work you need to create output as an instance of Matrix before this, so the full function would be:

def add(self,other):
    output = Matrix([[0 for x in range(self.m)] for y in range(self.m)])
    for i in range(self.m):
        for j in range(self.n): 
             output.rows[i][j] = self.rows[i][j] + other.rows[i][j]
    return output

Also as an aside if you are creating methods like add you should look into dunder methods (eg __add__ ); which will give you the nice functionality of being able to use the plus symbol to add instances of your object together.