### Approximating Periods of Modular Symbols on Weight Two Modular Forms

A modular symbol corresponds to an element of homology on a modular curve (relative to the cusps) and a weight two modular form corresponds to a holomorphic one-form. Given a modular symbol and a weight two modular form, how can I approximate the integral of the modular form over the relative cycle corresponding to the modular symbol?

An example (which fails to work) is the following:

f = Newforms(Gamma0(23), 2, names='a')[0];
M = ModularSymbols(23,2);
H=M.basis();
gamma=H[0];
f.period(gamma)