lookups.py 文件源码

def __init__(self, lhs, rhs):
        self.lhs, self.rhs = lhs, rhs
        self.rhs = self.get_prep_lookup()
        if hasattr(self.lhs, 'get_bilateral_transforms'):
            bilateral_transforms = self.lhs.get_bilateral_transforms()
        else:
            bilateral_transforms = []
        if bilateral_transforms:
            # We should warn the user as soon as possible if he is trying to apply
            # a bilateral transformation on a nested QuerySet: that won't work.
            # We need to import QuerySet here so as to avoid circular
            from django.db.models.query import QuerySet
            if isinstance(rhs, QuerySet):
                raise NotImplementedError("Bilateral transformations on nested querysets are not supported.")
        self.bilateral_transforms = bilateral_transforms