class_docstr: Helper class to allow construction of a list without
  having to reverse it in the end.
code: def __init__(self):
      self._head = _EMPTY_PLIST
      self._tail = _EMPTY_PLIST
  
imports: from ._compat import Sequence, Hashable
  from numbers import Integral
  from functools import reduce
label_desc: Use image node_id 1 to create a new _PListBuilder object from inherited base classes: object with example: obj = _PListBuilder()