docs: def set_instance(self, key, instance, default_scope=GlobalScope):
          '''
          Sets instance under specified provider key. If a provider for specified key does not exist, one is created
          without a factory using the given scope.
  
          :param key: Provider key
          :type key: object
          :param instance: Instance
          :type instance: object
          :param default_scope: Scope key, factory, or instance
          :type default_scope: object or callable
          '''
          if key not in self._providers:
              # We don't know how to create this kind of instance at this time, so add it without a factory.
              factory = None
              self.register_factory(key, factory, default_scope)
          self._providers[key].set_instance(instance)