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

    from .core import UnitBase
    if isinstance(wav, UnitBase):
        if (factor is None):
            raise ValueError(u'If    `wav`    is    specified    as    a    unit,    `factor`    should    be    set')
        wav = (factor * wav)
    c_Aps = _si.c.to_value((si.AA / si.s))
    h_cgs = _si.h.cgs.value
    hc = (c_Aps * h_cgs)
    f_la = (((cgs.erg / si.angstrom) / (si.cm ** 2)) / si.s)
    f_nu = (((cgs.erg / si.Hz) / (si.cm ** 2)) / si.s)
    nu_f_nu = ((cgs.erg / (si.cm ** 2)) / si.s)
    la_f_la = nu_f_nu
    phot_f_la = (astrophys.photon / (((si.cm ** 2) * si.s) * si.AA))
    phot_f_nu = (astrophys.photon / (((si.cm ** 2) * si.s) * si.Hz))
    L_nu = ((cgs.erg / si.s) / si.Hz)
    L_la = ((cgs.erg / si.s) / si.angstrom)
    nu_L_nu = (cgs.erg / si.s)
    la_L_la = nu_L_nu
    phot_L_la = (astrophys.photon / (si.s * si.AA))
    phot_L_nu = (astrophys.photon / (si.s * si.Hz))
    def converter(x):
        return (x * ((wav.to_value(si.AA, spectral()) ** 2) / c_Aps))
    def iconverter(x):
        return (x / ((wav.to_value(si.AA, spectral()) ** 2) / c_Aps))
    def converter_f_nu_to_nu_f_nu(x):
        return (x * wav.to_value(si.Hz, spectral()))
    def iconverter_f_nu_to_nu_f_nu(x):
        return (x / wav.to_value(si.Hz, spectral()))
    def converter_f_la_to_la_f_la(x):
        return (x * wav.to_value(si.AA, spectral()))
    def iconverter_f_la_to_la_f_la(x):
        return (x / wav.to_value(si.AA, spectral()))
    def converter_phot_f_la_to_f_la(x):
        return ((hc * x) / wav.to_value(si.AA, spectral()))
    def iconverter_phot_f_la_to_f_la(x):
        return ((x * wav.to_value(si.AA, spectral())) / hc)
    def converter_phot_f_la_to_f_nu(x):
        return ((h_cgs * x) * wav.to_value(si.AA, spectral()))
    def iconverter_phot_f_la_to_f_nu(x):
        return (x / (wav.to_value(si.AA, spectral()) * h_cgs))
    def converter_phot_f_la_phot_f_nu(x):
        return ((x * (wav.to_value(si.AA, spectral()) ** 2)) / c_Aps)
    def iconverter_phot_f_la_phot_f_nu(x):
        return ((c_Aps * x) /...

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

def spectral_density(wav, factor=None):