def _get_grouper(self, obj, validate=True):
self._set_grouper(obj)<EOL>self.grouper, exclusions, self.obj = _get_grouper(self.obj, [self.key],<EOL>axis=self.axis,<EOL>level=self.level,<EOL>sort=self.sort,<EOL>validate=validate)<EOL>return self.binner, self.grouper, self.obj<EOL>
Parameters
----------
obj : the subject object
validate : boolean, default True
    if True, validate the grouper

Returns
-------
a tuple of binner, grouper, obj (possibly sorted)