human
I wrote the below code

    (a1, b1) = lineseg.points[0]
    def x_axis_cut(ls):
        'Returns    the    point    where    the    input    line    segment\n                                intersects    the    x-axis.\n                                Parameters:\n                                ===========\n                                ls    :    Line    segment\n                                '
        (p, q) = ls.points
        if (p.y == S.Zero):
            return tuple(p)
        elif (q.y == S.Zero):
            return tuple(q)
        elif ((p.y / q.y) < S.Zero):
            return ((((p.y * (p.x - q.x)) / (q.y - p.y)) + p.x), S.Zero)
        else:
            return ()
    def y_axis_cut(ls):
        'Returns    the    point    where    the    input    line    segment\n                                intersects    the    y-axis.\n                                Parameters:\n                                ===========\n                                ls    :    Line    segment\n                                '
        (p, q) = ls.points
        if (p.x == S.Zero):
            return tuple(p)
        elif (q.x == S.Zero):
            return tuple(q)
        elif ((p.x / q.x) < S.Zero):
            return (S.Zero, (((p.x * (p.y - q.y)) / (q.x - p.x)) + p.y))
        else:
            return ()
    gens = (x, y)
    power_gens = {}
    for i in gens:
        power_gens[i] = S.Zero
    if (len(gens) > 1):
        if (len(gens) == 2):
            if (a[0] == S.Zero):
                if y_axis_cut(lineseg):
                    return (S.Zero, (b / a[1]))
                else:
                    return (a1, b1)
            elif (a[1] == S.Zero):
                if x_axis_cut(lineseg):
                    return ((b / a[0]), S.Zero)
                else:
                    return (a1, b1)
        if isinstance(expr, Expr):
            if expr.is_Add:
                for monomial in expr.args:
                    if monomial.is_Pow:
                        if (monomial.args[0] in gens):
                           ...

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

def best_origin(a, b, lineseg, expr):