Convert

def convert(self, obj):
        """Convert"""
        # We accept None representing No Image
        if obj is None:
            return None
        elif isinstance(obj, six.string_types):
            return DataFrame(filename=obj)
        elif isinstance(obj, DataFrame):
            return obj
        elif isinstance(obj, fits.HDUList):
            return DataFrame(frame=obj)
        elif isinstance(obj, fits.PrimaryHDU):
            return DataFrame(frame=fits.HDUList([obj]))
        else:
            msg = 'object of type %r cannot be converted to DataFrame' % obj
            raise TypeError(msg)