code: def open(self, filename=None):
          '''
          Open a browser tab with the notebook path specified relative to the
          notebook directory.
  
          If no filename is specified, open the root of the notebook server.
          '''
          if filename is None:
              address = self.address + 'tree'
          else:
              notebook_path = self.resource_filename(filename)
              if not notebook_path.isfile():
                  raise IOError('Notebook path not found: %s' % notebook_path)
              else:
                  address = '%snotebooks/%s' % (self.address, filename)
          webbrowser.open_new_tab(addressf open(self, filename=None):
          '''
          Open a browser tab with the notebook path specified relative to the
          notebook directory.
  
          If no filename is specified, open the root of the notebook server.
          '''
          if filename is None:
              address = self.address + 'tree'
          else:
              notebook_path = self.resource_filename(filename)
              if not notebook_path.isfile():
                  raise IOError('Notebook path not found: %s' % notebook_path)
              else:
                  address = '%snotebooks/%s' % (self.address, filename)
          webbrowser.open_new_tab(address)
docs: Open a browser tab with the notebook path specified relative to the
          notebook directory.
  
          If no filename is specified, open the root of the notebook server.