code: def pop(self, key, default=_marker):
          
          try:
              popped = self[key]
              del self[key]
              return popped
          except KeyError:
              if default == _marker:
                  raise
              return default
docs: remove the item by key
          If not default is specified, raise KeyError if nothing
          could be removed.
          Return 'default' if specified and nothing could be removed