def get_normalized_quantity_modifier(self, quantity):
modifier = self._quantity_modifiers.get(quantity, self._default_quantity_modifier)<EOL>if modifier is None:<EOL><INDENT>return (trivial_callable, quantity)<EOL><DEDENT>if callable(modifier):<EOL><INDENT>return (modifier, quantity)<EOL><DEDENT>if isinstance(modifier, (tuple, list)) and len(modifier) > <NUM_LIT:1> and callable(modifier[<NUM_LIT:0>]):<EOL><INDENT>return modifier<EOL><DEDENT>return (trivial_callable, modifier)<EOL>
Retrive a quantify modifier, normalized.
This function would also return a tuple, with the first item a callable,
and the rest native quantity names

Parameters
----------
quantity : str
    name of the derived quantity to get

Returns
-------
tuple : (callable, quantity1, quantity2...)