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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 get(self, rule, default=None):
 """Return the existing version of the given rule. If the rule is not present in the classifier set, return the default. If no default was given, use None. This is useful for eliminating duplicate copies of rules. Usage: unique_rule = model.get(possible_duplicate, possible_duplicate) Arguments: rule: The ClassifierRule instance which may be a duplicate of another already contained in the classifier set. default: The value returned if the rule is not a duplicate of another already contained in the classifier set. Return: If the rule is a duplicate of another already contained in the classifier set, the existing one is returned. Otherwise, the value of default is returned. """

        assert isinstance(rule, ClassifierRule)

        if (rule.condition not in self._population or
                rule.action not in self._population[rule.condition]):
            return default
        return self._population[rule.condition][rule.action]