In numpy v1.7+, you can take advantage of the "where" option for ufuncs. You can do things in one line and you don't have to deal with the errstate context manager.
>>> a = np.array([-1, 0, 1, 2, 3], dtype=float) >>> b = np.array([ 0, 0, 0, 2, 2], dtype=float) # If you don't pass `out` the indices where (b == 0) will be uninitialized! >>> c = np.divide(a, b, out=np.zeros_like(a), where=b!=0) >>> print(c) [ 0. 0. 0. 1. 1.5]
In this case, it does the divide calculation anywhere 'where' b does not equal zero. When b does equal zero, then it remains unchanged from whatever value you originally gave it in the 'out' argument.