Which one is better?

better.py

chi = Function('chi')(x, y)
chix = chi.diff(x)
chiy = chi.diff(y)
cpde = chix + h*chiy - hy*chi
chieq = Symbol("chi")
for i in range(1, deg + 1):
    chieq += Add(*[
        Symbol("chi_" + str(power) + "_" + str(i - power))*x**power*y**(i - power)
        for power in range(i + 1)])
        cnum, cden = cancel(chieq.diff(x) + h*chieq.diff(y)
            - hy*chieq).as_numer_denom() # Is this better
        cnum, cden = cancel(cpde.subs({chi : chieq}).doit()).as_numer_denom()  ## Or this?