'Adds to the set of units enabled in the unit registry.
These units are searched when using
`UnitBase.find_equivalent_units`, for example.
Parameters
units : list of sequences, dicts, or modules containing units, or units
This is a list of things in which units may be found
(sequences, dicts or modules), or units themselves.  The
entire set will be added to the "enabled" set for
searching through by methods like
`UnitBase.find_equivalent_units` and `UnitBase.compose`.'

def add_enabled_units(self, units):

    units = _flatten_units_collection(units)
    for unit in units:
        for st in unit._names:
            if ((st in self._registry) and (unit != self._registry[st])):
                raise ValueError(u'Object    with    name    {0!r}    already    exists    in    namespace.    Filter    the    set    of    units    to    avoid    name    clashes    before    enabling    them.'.format(st))
        for st in unit._names:
            self._registry[st] = unit
        self._all_units.add(unit)
        if (not isinstance(unit, PrefixUnit)):
            self._non_prefix_units.add(unit)
        hash = unit._get_physical_type_id()
        self._by_physical_type.setdefault(hash, set()).add(unit)
