http://quantlib.414.s1.nabble.com/Python-Saving-Interest-Rate-Curve-Objects-to-File-tp17751p17758.html
You can instantiate an interpolated curve. The actual type depends on which kind of curve you bootstrapped to begin with. If you used a PiecewiseFlatForward and you stored the (date, forward) nodes, you can use them to create a ForwardCurve instance. If you bootstrapped a curve that interpolates discounts or zero yields, you might have to add the corresponding class to the SWIG interfaces and export it. In general: first, look at piecewiseyieldcurve.i and find out what kind of curve you used; for instance, the lines
export_piecewise_curve(PiecewiseFlatForward,ForwardRate,BackwardFlat);
export_piecewise_curve(PiecewiseLogCubicDiscount,Discount,MonotonicLogCubic);
tell you that PiecewiseFlatForward uses BackwardFlat interpolation on (instantaneous) forward rates, and PiecewiseLogCubicDiscount uses MonotonicLogCubic interpolation on discounts. Then look into forwardcurve.i if you're interpolating forwards, discountcurve.i for discounts and zerocurve.i for zero rates. If you find a line in there corresponding to the interpolation you used for the bootstrap, you're all set; for instance, if you used PiecewiseFlatForward, you'll see
export_forward_curve(ForwardCurve,BackwardFlat);
that tells you that you can use ForwardCurve, which has the same interpolation. If there's no such line, you'll have to add it; for instance, if you used PiecewiseLogCubicDiscount, you'll have to add a line like
export_discount_curve(MyDiscountCurve,MonotonicLogCubic);
to discount.i and rebuild the interfaces (MonotonicLogCubic is the interpolation; MyDiscountCurve is the name that you want to use for the curve and you can change it to whatever you want).
Hope this helps,
Luigi