human
Here's a good function header given the following:
I wrote the below code

    from sympy.core.symbol import Dummy
    from sympy.solvers import solve
    period = []
    x = Dummy('x')
    def untillist(cf):
        for nxt in cf:
            if isinstance(nxt, list):
                period.extend(nxt)
                (yield x)
                break
            (yield nxt)
    a = Integer(0)
    for a in continued_fraction_convergents(untillist(cf)):
        pass
    if period:
        y = Dummy('y')
        solns = solve((continued_fraction_reduce((period + [y])) - y), y)
        solns.sort()
        pure = solns[(-1)]
        return a.subs(x, pure).radsimp()
    else:
        return a

What's a good function header?
assistant
#Here's a good function header.

def continued_fraction_reduce(cf):