I have a 3-dimensional array in python, and would like to learn how to find and replace given elements

For example, 

```
x = np.array([[1, 1, 1, 0], [0, 5, 0, 1], [2, 1, 3, 10]], np.int32)

```

I'd like to replace each 0 with x in the array, which would result in:

```
([[1,1,1,x], [x,5,x,1], [2,1,3,10]])

```

This is where I am at, but I get an error due to 'x' not being an integer

import numpy as np
x = np.array([[1,1,1,0],[0,5,0,1],[2,1,3,10]])
x[x==0] = 'x'
print (x)