make urllib.response.addinfourl instantiable (#2134)

Fixes #1377 (because HTTPError is a subclass of addinfourl). Also part of #1476.

stdlib/3/urllib/response.pyi

@@ -1,11 +1,41 @@
 # private module, we only expose what's needed
 
-from typing import BinaryIO, Mapping, Optional
+from typing import BinaryIO, Iterable, List, Mapping, Optional, Type, TypeVar
 from types import TracebackType
 
-class addinfourl(BinaryIO):
-    headers = ...  # type: Mapping[str, str]
-    url = ...  # type: str
-    code = ...  # type: int
+_AIUT = TypeVar("_AIUT", bound=addbase)
+
+class addbase(BinaryIO):
+    def __enter__(self: _AIUT) -> _AIUT: ...
+    def __exit__(self, type: Optional[Type[BaseException]], value: Optional[BaseException], traceback: Optional[TracebackType]) -> bool: ...
+    def __iter__(self: _AIUT) -> _AIUT: ...
+    def __next__(self) -> bytes: ...
+    def close(self) -> None: ...
+    # These methods don't actually exist, but the class inherits at runtime from
+    # tempfile._TemporaryFileWrapper, which uses __getattr__ to delegate to the
+    # underlying file object. To satisfy the BinaryIO interface, we pretend that this
+    # class has these additional methods.
+    def fileno(self) -> int: ...
+    def flush(self) -> None: ...
+    def isatty(self) -> bool: ...
+    def read(self, n: int = ...) -> bytes: ...
+    def readable(self) -> bool: ...
+    def readline(self, limit: int = ...) -> bytes: ...
+    def readlines(self, hint: int = ...) -> List[bytes]: ...
+    def seek(self, offset: int, whence: int = ...) -> int: ...
+    def seekable(self) -> bool: ...
+    def tell(self) -> int: ...
+    def truncate(self, size: Optional[int] = ...) -> int: ...
+    def writable(self) -> bool: ...
+    def write(self, s: bytes) -> int: ...
+    def writelines(self, lines: Iterable[bytes]) -> None: ...
+
+class addinfo(addbase):
+    headers: Mapping[str, str]
     def info(self) -> Mapping[str, str]: ...
+
+class addinfourl(addinfo):
+    url: str
+    code: int
     def geturl(self) -> str: ...
+    def getcode(self) -> int: ...