code: def bind(self, container):
          
          # if there's already a matching bound instance, return that
          shared = container.shared_extensions.get(self.sharing_key)
          if shared:
              return shared
  
          instance = super(SharedExtension, self).bind(container)
  
          # save the new instance
          container.shared_extensions[self.sharing_key] = instance
  
          return instance
docs: Bind implementation that supports sharing.