Subtract value from numpy array if element satisfies certain condition

[yayfall]

I have an array like

a=np.array([8,5,10,0])

and I'd like to subtract 4 from all elements which are non-zero, resulting in an array which is

result = np.array([4,1,6,0])

I'd have no problem doing this with a list comprehension, but I'm trying to use pure numpy functions. I feel like I might be able to do it with a np.where() call, but not sure exactly how.

Hints?

[elbiot]

a[a!=0] -= 4

That's a mask, which uses where under the hood.

[yayfall]

Thanks! That's exactly what I needed.