PurePath.parent[s] should be properties (#706)

PurePath.parent[s] should be properties

Author: gvanrossum

stdlib/3.5/pathlib.pyi

@@ -3,7 +3,7 @@
 from typing import Any, Generator, IO, Optional, Sequence, Tuple, Type, TypeVar, Union
 import os
 
-_P = TypeVar('_P', 'PurePath')
+_P = TypeVar('_P', bound='PurePath')
 
 class PurePath:
     parts = ...  # type: Tuple[str, ...]
@@ -31,7 +31,9 @@ class PurePath:
     def with_name(self: _P, name: str) -> _P: ...
     def with_suffix(self: _P, suffix: str) -> _P: ...
     def joinpath(self: _P, *other: Union[str, PurePath]) -> _P: ...
+    @property
     def parents(self: _P) -> Sequence[_P]: ...
+    @property
     def parent(self: _P) -> _P: ...
 
 class PurePosixPath(PurePath): ...