StringPolynomial Issue for a general polynomial representation

[olgOk]

Hi!

I was trying to play with the example for an arbitrary function specified as a string using a numpy expression when run into an issue for the code line (poly + Polynomial([0, ] * poly.degree() + [eps / 2, ]))

TypeError: unsupported operand type(s) for +: 'StringPolynomial' and 'Polynomial'

My code followed exactly the example provided in the repo:

poly = pyqsp.poly.StringPolynomial("np.cos(3*x)", 6)
ang_seq = pyqsp.angle_sequence.QuantumSignalProcessingPhases(poly)
pyqsp.response.PlotQSPResponse(ang_seq, target=poly, signal_operator="Wx")

Are there missing lines of code that convert a string representation of a function to a function or am I doing something wrong here?