In this example, we will learn how to use loops to add two 3×3 matrices and return the sum matrix with Python.

### Source Code

```
#! /usr/bin/env python3
# -*- coding: utf-8 -*-
# Define two matrix
X = [[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
Y = [[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
# Initialize sum matrix
sum = [[0, 0, 0],
[0, 0, 0],
[0, 0, 0]]
# loop through rows
for i in range(len(X)):
# loop through column
for j in range(len(X[0])):
sum[i][j] = X[i][j] + Y[i][j]
# print out results
print('Sum of X and Y:')
for r in sum:
print(r)
```

Output:

```
Sum of X and Y:
[2, 4, 6]
[8, 10, 12]
[14, 16, 18]
```