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django-authority / authority / exceptions.py

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class AuthorityException(Exception):
    pass

class NotAModel(AuthorityException):
    def __init__(self, object):
        super(NotAModel, self).__init__(
            "Not a model class or instance")

class UnsavedModelInstance(AuthorityException):
    def __init__(self, object):
        super(UnsavedModelInstance, self).__init__(
            "Model instance has no pk, was it saved?")