In Python how would I implement a function that returns the product of two matrices. if the dimensions of the input matrices are incompatible, print an error message and return $`$None$`.$ Use $`$numpy$`$ for this problem.

below are the test cases I have and the beginning of the code:

# TODO: implement this function

def matrix$\_$mult $($A: Matrix, B: Matrix$)->$ Matrix:

return $[[]]$

# test cases

A $=[[1,2,3],$

$[4,5,6]]$

At $=[[1,4],$

$[2,5],$

$[3,6]]$

I $=[[1,0],$

$[0,1]]$

A$\_$At $=[[14,32],$

$[32,77]]$

At$\_$A $=[[17,22,27],$

$[22,29,36],$

$[27,36,45]]$

# the matrices A$,$ At$,$ and I are declared in problem $9$

assert matrix$\_$mult $($A$,$ At$)==$ A$\_$At

assert matrix$\_$mult $($At$,$ A$)==$ At$\_$A

assert matrix$\_$mult $($I$,$ A$)==$ A

assert matrix$\_$mult $($At$,$ I$)==$ At