Matrix understanding in Python

[RavCOder]

Hi,
this is text of exercise:

Given a 2D grid, each cell is either a zombie 1 or a human 0. Zombies can turn adjacent (up / down / left / right) human beings into zombies every hour. Find out how many hours does it take to infect all humans?

I haven't found many resources on the 2d matrices in python ,so
I tried to break it down by thinking if I had a list rather than a matrix:
if I had only one list and had to change the element with a value of 0 to 1 I found this solution that works and returns a list with all the values ​​1

a = [0,1,1,0,1]
contagion = [1 if x == 0 else x for x in a]
print(contagion)

It also works for others (I did the tests)

But how do I get a matrix and then "calculate" how long it takes for it to become all of them?