code: def register(self, entry_point):
          
          if entry_point in self.registered_extensions:
              raise ValueError('Extension already registered')
  
          ep = EntryPoint.parse(entry_point)
          if ep.name in self.names():
              raise ValueError('An extension with the same name already exist')
  
          ext = self._load_one_plugin(ep, False, (), {}, False)
          self.extensions.append(ext)
          if self._extensions_by_name is not None:
              self._extensions_by_name[ext.name] = ext
          self.registered_extensions.insert(0, entry_point)
docs: Register an extension
  
          :param str entry_point: extension to register (entry point syntax).
          :raise: ValueError if already registered.