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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_cache(self):
 """ If one of the original registries was changed. Update our merged version. """

        expected_version = (
            tuple(r._version for r in self.registries) +
            (self._extra_registry._version, ))

        if self._last_version != expected_version:
            registry2 = Registry()

            for reg in self.registries:
                registry2.key_bindings.extend(reg.key_bindings)

            # Copy all bindings from `self._extra_registry`.
            registry2.key_bindings.extend(self._extra_registry.key_bindings)

            self._registry2 = registry2
            self._last_version = expected_version