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

    def _trace_single_line1(t):
        t = t.sorted_components()
        components = t.components
        ncomps = len(components)
        g = LorentzIndex.metric
        hit = 0
        for i in range(ncomps):
            if (components[i] == GammaMatrix):
                hit = 1
                break
        for j in range((i + hit), ncomps):
            if (components[j] != GammaMatrix):
                break
        else:
            j = ncomps
        numG = (j - i)
        if (numG == 0):
            tcoeff = t.coeff
            return (t.nocoeff if tcoeff else t)
        if ((numG % 2) == 1):
            return TensMul.from_data(S.Zero, [], [], [])
        elif (numG > 4):
            a = t.split()
            ind1 = a[i].get_indices()[0]
            ind2 = a[(i + 1)].get_indices()[0]
            aa = (a[:i] + a[(i + 2):])
            t1 = (tensor_mul(*aa) * g(ind1, ind2))
            t1 = t1.contract_metric(g)
            args = [t1]
            sign = 1
            for k in range((i + 2), j):
                sign = (- sign)
                ind2 = a[k].get_indices()[0]
                aa = ((a[:i] + a[(i + 1):k]) + a[(k + 1):])
                t2 = ((sign * tensor_mul(*aa)) * g(ind1, ind2))
                t2 = t2.contract_metric(g)
                t2 = simplify_gpgp(t2, False)
                args.append(t2)
            t3 = TensAdd(*args)
            t3 = _trace_single_line(t3)
            return t3
        else:
            a = t.split()
            t1 = _gamma_trace1(*a[i:j])
            a2 = (a[:i] + a[j:])
            t2 = tensor_mul(*a2)
            t3 = (t1 * t2)
            if (not t3):
                return t3
            t3 = t3.contract_metric(g)
            return t3
    if isinstance(t, TensAdd):
        a = [(_trace_single_line1(x) * x.coeff) for x in t.args]
        return TensAdd(*a)
    elif isinstance(t, (Tensor, TensMul)):
        r = (t.coeff * _trace_single_line1(t))
        return r
    else:
        return trace(t)

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

def _trace_single_line(t):