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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 register_identity(self, category, type_, *, names={}):
 """ Register an identity with the given `category` and `type_`. If there is already a registered identity with the same `category` and `type_`, :class:`ValueError` is raised. `names` may be a mapping which maps :class:`.structs.LanguageTag` instances to strings. This mapping will be used to produce ``<identity/>`` declarations with the respective ``xml:lang`` and ``name`` attributes. """

        key = category, type_
        if key in self._identities:
            raise ValueError("identity already claimed: {!r}".format(key))
        self._identities[key] = names
        self.on_info_changed()