Unify stdlib/{2,3}/typing.pyi

Also fix signature of IO.seek, IO.truncate, IO.write, and MutableMapping.update
Fixes #1016

Note: I couldn't put typing.pyi in 2and3 because of an import cycle when adding `import sys` to 2/typing.pyi

stdlib/2/typing.pyi

@@ -13,11 +13,12 @@ Tuple = object()
 Callable = object()
 Type = object()
 _promote = object()
+no_type_check = object()
 ClassVar = object()
 
 class GenericMeta(type): ...
 
-# Type aliases
+# Type aliases and type constructors
 
 class TypeAlias:
     # Class for defining generic aliases for library types.
@@ -57,6 +58,10 @@ class SupportsFloat(metaclass=ABCMeta):
     @abstractmethod
     def __float__(self) -> float: ...
 
+class SupportsComplex(metaclass=ABCMeta):
+    @abstractmethod
+    def __complex__(self) -> complex: ...
+
 class SupportsAbs(Generic[_T]):
     @abstractmethod
     def __abs__(self) -> _T: ...
@@ -73,6 +78,13 @@ class Sized(metaclass=ABCMeta):
     @abstractmethod
     def __len__(self) -> int: ...
 
+class Hashable(metaclass=ABCMeta):
+    # TODO: This is special, in that a subclass of a hashable class may not be hashable
+    #   (for example, list vs. object). It's not obvious how to represent this. This class
+    #   is currently mostly useless for static checking.
+    @abstractmethod
+    def __hash__(self) -> int: ...
+
 class Iterable(Generic[_T_co]):
     @abstractmethod
     def __iter__(self) -> Iterator[_T_co]: ...
@@ -89,7 +101,9 @@ class Generator(Iterator[_T_co], Generic[_T_co, _T_contra, _V_co]):
     def send(self, value: _T_contra) -> _T_co: ...
 
     @abstractmethod
-    def throw(self, typ: BaseException, val: Any = None, tb: Any = None) -> None: ...
+    def throw(self, typ: Type[BaseException], val: Optional[BaseException] = None,
+              # TODO: tb should be TracebackType but that's defined in types
+              tb: Any = None) -> None: ...
 
     @abstractmethod
     def close(self) -> None: ...
@@ -121,8 +135,12 @@ class MutableSequence(Sequence[_T], Generic[_T]):
     @overload
     @abstractmethod
     def __setitem__(self, s: slice, o: Iterable[_T]) -> None: ...
+    @overload
     @abstractmethod
-    def __delitem__(self, i: Union[int, slice]) -> None: ...
+    def __delitem__(self, i: int) -> None: ...
+    @overload
+    @abstractmethod
+    def __delitem__(self, i: slice) -> None: ...
     # Mixin methods
     def append(self, object: _T) -> None: ...
     def extend(self, iterable: Iterable[_T]) -> None: ...
@@ -242,18 +260,18 @@ class IO(Iterator[AnyStr], Generic[AnyStr]):
     @abstractmethod
     def readlines(self, hint: int = ...) -> list[AnyStr]: ...
     @abstractmethod
-    def seek(self, offset: int, whence: int = ...) -> None: ...
+    def seek(self, offset: int, whence: int = ...) -> int: ...
     @abstractmethod
     def seekable(self) -> bool: ...
     @abstractmethod
     def tell(self) -> int: ...
     @abstractmethod
-    def truncate(self, size: int = ...) -> Optional[int]: ...
+    def truncate(self, size: Optional[int] = ...) -> int: ...
     @abstractmethod
     def writable(self) -> bool: ...
     # TODO buffer objects
     @abstractmethod
-    def write(self, s: AnyStr) -> None: ...
+    def write(self, s: AnyStr) -> int: ...
     @abstractmethod
     def writelines(self, lines: Iterable[AnyStr]) -> None: ...
 
@@ -290,6 +308,8 @@ class TextIO(IO[unicode]):
     @abstractmethod
     def __enter__(self) -> TextIO: ...
 
+class ByteString(Sequence[int]): ...
+
 class Match(Generic[AnyStr]):
     pos = 0
     endpos = 0