A query to check if this query field is one of the values
            in ``values``.  Produces a MongoDB ``$in`` expression.

def in_(self, *values):
        ''' A query to check if this query field is one of the values
            in ``values``.  Produces a MongoDB ``$in`` expression.
        '''
        return QueryExpression({
            self : { '$in' : [self.get_type().wrap_value(value) for value in values] }
        })