def combine_docstrings(cls):
    """ Combine the docstrings of a method and earlier implementations of the same method in parent classes """
    for name, func in cls.__dict__.items():
        if name == 'calc_psf':
            jwinstrument_class = cls
            spacetelescope_class = cls.__base__
            ind0 = getattr(jwinstrument_class, 'calc_psf').__doc__.index(
                'add_distortion')
            ind1 = getattr(spacetelescope_class, 'calc_psf').__doc__.index(
                'Returns')
            func.__doc__ = getattr(spacetelescope_class, 'calc_psf').__doc__[
                0:ind1] + getattr(jwinstrument_class, 'calc_psf').__doc__[ind0:
                ] + getattr(spacetelescope_class, 'calc_psf').__doc__[ind1:]
    return cls
