def binned_source_to_rest(spec: Spectrum, z: float = None) -> Spectrum:
"""
Takes in a binned source spectrum and shifts it to rest frame.
WARNING: Assumes desired wavelengths will be integer values and called (int) on them as a result. If integer
wavelengths are NOT desired, this method will need to be modified.
:param spec: Binned source spectrum
:type spec: Spectrum
:param z: Original redshift. If not passed, it will call spec.getRS() and use that value.
:type z: float
:return: Rest frame spectrum
:rtype: Spectrum
"""
spec = spec.cpy()
z = z or spec.getRS()
wls = spec.getWavelengths()
n = len(wls)
for wl in wls:
spec[int(wl / (1 + z))] = spec[wl]
del spec[wl]
return spec
