I'm having trouble adding two matrices in python - isa-swizzling

Question

I want to add two matrcies in python 3 but the problem comes when I add input to the program
Here is my code
def addmatrix(a,b):
d=[]
n=0
while n < len (a):
c = []
k = 0
while k < len (a[0]) :
c.append(a[n][k]+b[n][k])
k += 1
n += 1
d.append (c)
return d
def main():
a = input("Enter a Matrix: ")
b = input("Enter another Matrix: ")
print (addmatrix(a,b))
main()
If the input is
Enter a Matrix: [[5,6], [1,2], [2,4]]
Enter another Matrix: [[2,3], [-6,0], [-2, 4]]
The output comes out as [['[['], ['[['], ['52'], [',,'], ['63'], [']]'], [',,'], [' '], ['[['], ['1-'], [',6'], ['2,'], [']0'], [',]'], [' ,'], ['[ '], ['2['], [',-'], ['42'], ['],'], ['] ']]
But if I take out the input from the program and make it so that
def main():
a = [[5,6], [1,2], [2,4]]
b = [[2,3], [-6,0], [-2, 4]]
print (addmatrix(a,b))
main()
The output then comes out as [[7, 9], [-5, 2], [0, 8]] which is correct.
Is there a way I can make my program work so that when a person inputs two matrices they add together? I'm new at python so any help will be appreciated :)

Answer 1

You will have to convert the user input into a Python object. Right now, it's a string.
You can use eval (which should not be used if you don't know what your users will input. I can type in __import__('os').system('rm /some/file.txt') and Python will delete a file):
a = eval(input("Enter a Matrix: "))
Or you can use ast.literal_eval, which is safe:
from ast import literal_eval
...
a = literal_eval(input("Enter a Matrix: "))

Answer 2

Try this:
import ast
def addmatrix(a,b):
return [map(sum, zip(*x)) for x in zip(a,b)]
def main():
a = ast.literal_eval(raw_input("Enter a Matrix: "))
b = ast.literal_eval(raw_input("Enter another Matrix: "))
print addmatrix(a,b)
main()