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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 _finalize_namespaces(self, ns_dict=None):
 """Returns a dictionary of namespaces to be exported with an XML document. This loops over all the namespaces that were discovered and built during the execution of ``collect()`` and ``_parse_collected_classes()`` and attempts to merge them all. Raises: .namespaces.DuplicatePrefixError: If namespace prefix was mapped to more than one namespace. .namespaces.NoPrefixError: If a namespace was collected that is not mapped to a prefix. """

        if ns_dict:
            # Add the user's entries to our set
            for ns, alias in six.iteritems(ns_dict):
                self._collected_namespaces.add_namespace_uri(ns, alias)

        # Add the ID namespaces
        self._collected_namespaces.add_namespace_uri(
            ns_uri=idgen.get_id_namespace(),
            prefix=idgen.get_id_namespace_alias()
        )

        # Remap the example namespace to the one expected by the APIs if the
        # sample example namespace is found.
        self._fix_example_namespace()

        # Add _input_namespaces
        for prefix, uri in six.iteritems(self._input_namespaces):
            self._collected_namespaces.add_namespace_uri(uri, prefix)

        # Add some default XML namespaces to make sure they're there.
        self._collected_namespaces.import_from(namespaces.XML_NAMESPACES)

        # python-stix's generateDS-generated binding classes can't handle
        # default namespaces.  So make sure there are no preferred defaults in
        # the set.  Get prefixes from the global namespace set if we have to.
        for ns_uri in self._collected_namespaces.namespace_uris:
            preferred_prefix = self._collected_namespaces.preferred_prefix_for_namespace(ns_uri)

            if preferred_prefix:
                continue

            # No preferred prefix set for namespace. Try to assign one.
            prefixes = self._collected_namespaces.get_prefixes(ns_uri)

            if prefixes:
                prefix = next(iter(prefixes))
            else:
                prefix = namespaces.lookup_name(ns_uri)

            if prefix is None:
                raise namespaces.NoPrefixesError(ns_uri)

            self._collected_namespaces.set_preferred_prefix_for_namespace(
                ns_uri=ns_uri,
                prefix=prefix,
                add_if_not_exist=True
            )