'Typecheck and fix up some arguments supplied to various methods.
Specifically: ensure that \'objects\' is a list; if output_dir is
None, replace with self.output_dir.  Return fixed versions of
\'objects\' and \'output_dir\'.'

def _fix_object_args(self, objects, output_dir):

    if (not isinstance(objects, (list, tuple))):
        raise TypeError("'objects'    must    be    a    list    or    tuple    of    strings")
    objects = list(objects)
    if (output_dir is None):
        output_dir = self.output_dir
    elif (not isinstance(output_dir, str)):
        raise TypeError("'output_dir'    must    be    a    string    or    None")
    return (objects, output_dir)
