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

    if (initial_color is None):
        initial_color = (0 if clip.ismask else [0, 0, 0])
    initial_color = np.array(initial_color)
    def fl(gf, t):
        if (t >= duration):
            return gf(t)
        else:
            fading = ((1.0 * t) / duration)
            return ((fading * gf(t)) + ((1 - fading) * initial_color))
    return clip.fl(fl)

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

def fadein(clip, duration, initial_color=None):