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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 update(self, key, value):
 """Updates the map by updating the value of a key :type key: :class: '~opencensus.tags.tag_key.TagKey' :param key: A tag key to be updated :type value: :class: '~opencensus.tags.tag_value.TagValue' :param value: The value to update the key to in the map """

        if key in self.map:
            self.map[key] = value