Natural spline with constant extrapolation in python

Ive been using the following code to interpolate with constant extrapolation in the past

from scipy import interpolate
f = interpolate.InterpolatedUnivariateSpline(x,y, k = 3, ext = 3)  

but the spline is 'not-a-knot' instead of 'natural'. Now, I know that it is possible to perform natural spline interpolation using

from scipy import interpolate
f = interpolate.CubicSpline(x,y, bc_type =  'natural')  

but I don't see an option to add constant extrapolation.

Is there a function/way to do both features at the same time (natural+constant extrapolation)?

Thanks!