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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def instances(self, skip_exist_test=False):
 """ Ask the collection to return a list of instances. If skip_exist_test is set to True, the instances returned by the collection won't have their primary key checked for existence. """

        self.reset_result_type()
        self._instances = True
        self._instances_skip_exist_test = skip_exist_test
        return self