Interpolation with SciPy

This didn't take long, thanks to SciPy.

from scipy.interpolate import interpolate as interp

xa = [i * 10 for i in range(10)]
ya = [200.0 + 1.5 * x for x in xa]

iobj = interp.interp1d(xa, ya)
i_xa = [i for i in range(90)]
i_ya = [iobj(x) for x in i_xa]

import pylab as pl
pl.plot(xa, ya, "o")
pl.plot(i_xa, i_ya, "-")
pl.ylim(0, 1000)
pl.show()