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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 quality(self, key):
 """Returns the quality of the key. .. versionadded:: 0.6 In previous versions you had to use the item-lookup syntax (eg: ``obj[key]`` instead of ``obj.quality(key)``) """

        for item, quality in self:
            if self._value_matches(key, item):
                return quality
        return 0