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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 tag(self, name, formatter=None):
 """Return instance of Tag. Args: name (str):
 The value for this tag. formatter (method, optional):
 A method that take a tag value and returns a formatted tag. Returns: obj: An instance of Tag. """

        tag = Tag(name, formatter)
        for tag_data in self._tags:
            if tag_data.name == name:
                tag = tag_data
                break
        else:
            self._tags.append(tag)
        return tag