Numpy where and division by zero

Question

I need to compute x in the following way (legacy code):

x = numpy.where(b == 0, a, 1/b) 

I suppose it worked in python-2.x (as

Answer 1

If you wish to disable warnings in numpy while you divide by zero, then do something like:

>>> existing = numpy.seterr(divide="ignore")
>>> # now divide by zero in numpy raises no sort of exception
>>> 1 / numpy.zeros( (2, 2) )
array([[ inf,  inf],
       [ inf,  inf]])
>>> numpy.seterr(*existing)

Of course this only governs division by zero in an array. It will not prevent an error when doing a simple 1 / 0.

In your particular case, if we wish to ensure that we work whether b is a scalar or a numpy type, do as follows:

# ignore division by zero in numpy
existing = numpy.seterr(divide="ignore")

# upcast `1.0` to be a numpy type so that numpy division will always occur
x = numpy.where(b == 0, a, numpy.float64(1.0) / b) 

# restore old error settings for numpy
numpy.seterr(*existing)