[SciPy-User] Writing an Interpolation Function to Disk?

[Pauli Virtanen]

On Fri, 25 Feb 2011 12:42:47 +0100, Sloan Lindsey wrote:
> I've been using the new interpolation routines
> (scipy.interpolate.CloughTocher2DInterpolator) quite happily in my
> project but I'm wondering if there is a way to save the output from the
> interpolation function to disk. I'm using rather large datasets
> (200,000+ points) and it takes an appreciable time to recalculate the
> interpolant every time that I run my program. 

I assume most of the time is taken by constructing the Delaunay 
triangulation (scipy.spatial.Delaunay(points)).

> I'd like it if I could
> dump the baked interpolant to disk and then restore it on execution. Of
> course I probably need to generate the interpolant per machine but I can
> deal with that. Is there any cool way to do this?

Ideally, this would work:

	import pickle
	f = open('file.pck', 'wb')
	pickle.dump(interpolator, f)
	f.close()

but it doesn't work, since there's a small unnecessary technical snatch 
(scipy.spatial.interpnd has the wrong __name__). This will be fixed in 
the next version of Scipy, so a small workaround is needed in the 
meantime:

class PickleableInterpolator(CloughTocher2DInterpolator):
    def __getstate__(self):
        return (self.tri, self.values, self.grad, self.is_complex,
                self.fill_value, self.values_shape)
    def __setstate__(self, data):
        self.tri, self.values, self.grad, self.is_complex, \
                  self.fill_value, self.values_shape = data
        self.points = self.tri.points

This kind of mucking around might break in future Scipy versions, so I 
suggest you put it in 'if scipy.__version__ == "0.9.0":'

Note that pickling objects like this is quite brittle --- the internal 
details of what needs to be pickled may change, so do not expect the 
pickle files to work across different Scipy versions.

-- 
Pauli Virtanen