code: def change_mpl_backend(self, command):
          
          if command.startswith('%matplotlib') and \
            len(command.splitlines()) == 1:
              if not 'inline' in command:
                  self.silent_execute(command)
docs: If the user is trying to change Matplotlib backends with
          %matplotlib, send the same command again to the kernel to
          correctly change it.
  
          Fixes issue 4002