Annotate pathlib.Path methods as returning the same type even when su…

…bclassed. (python#4755)

stdlib/3/pathlib.pyi

@@ -61,7 +61,7 @@ class PureWindowsPath(PurePath): ...
 
 class Path(PurePath):
     def __new__(cls: Type[_P], *args: Union[str, _PathLike], **kwargs: Any) -> _P: ...
-    def __enter__(self) -> Path: ...
+    def __enter__(self: _P) -> _P: ...
     def __exit__(
         self, exc_type: Optional[Type[BaseException]], exc_value: Optional[BaseException], traceback: Optional[TracebackType]
     ) -> Optional[bool]: ...
@@ -70,7 +70,7 @@ class Path(PurePath):
     def stat(self) -> os.stat_result: ...
     def chmod(self, mode: int) -> None: ...
     def exists(self) -> bool: ...
-    def glob(self, pattern: str) -> Generator[Path, None, None]: ...
+    def glob(self: _P, pattern: str) -> Generator[_P, None, None]: ...
     def group(self) -> str: ...
     def is_dir(self) -> bool: ...
     def is_file(self) -> bool: ...
@@ -81,7 +81,7 @@ class Path(PurePath):
     def is_fifo(self) -> bool: ...
     def is_block_device(self) -> bool: ...
     def is_char_device(self) -> bool: ...
-    def iterdir(self) -> Generator[Path, None, None]: ...
+    def iterdir(self: _P) -> Generator[_P, None, None]: ...
     def lchmod(self, mode: int) -> None: ...
     def lstat(self) -> os.stat_result: ...
     def mkdir(self, mode: int = ..., parents: bool = ..., exist_ok: bool = ...) -> None: ...
@@ -154,7 +154,7 @@ class Path(PurePath):
         def rename(self, target: Union[str, PurePath]) -> None: ...
         def replace(self, target: Union[str, PurePath]) -> None: ...
     def resolve(self: _P, strict: bool = ...) -> _P: ...
-    def rglob(self, pattern: str) -> Generator[Path, None, None]: ...
+    def rglob(self: _P, pattern: str) -> Generator[_P, None, None]: ...
     def rmdir(self) -> None: ...
     def symlink_to(self, target: Union[str, Path], target_is_directory: bool = ...) -> None: ...
     def touch(self, mode: int = ..., exist_ok: bool = ...) -> None: ...