asyncio: Modernize type annotations

tornado/platform/asyncio.py

@@ -36,23 +36,33 @@ import warnings
 from tornado.gen import convert_yielded
 from tornado.ioloop import IOLoop, _Selectable
 
-from typing import Any, TypeVar, Awaitable, Callable, Union, Optional, List, Dict
-
-if typing.TYPE_CHECKING:
-    from typing import Set, Tuple  # noqa: F401
-    from typing_extensions import Protocol
+from typing import (
+    Any,
+    Awaitable,
+    Callable,
+    Dict,
+    List,
+    Optional,
+    Protocol,
+    Set,
+    Tuple,
+    TypeVar,
+    Union,
+)
+
+
+class _HasFileno(Protocol):
+    def fileno(self) -> int:
+        pass
 
-    class _HasFileno(Protocol):
-        def fileno(self) -> int:
-            pass
 
-    _FileDescriptorLike = Union[int, _HasFileno]
+_FileDescriptorLike = Union[int, _HasFileno]
 
 _T = TypeVar("_T")
 
 
 # Collection of selector thread event loops to shut down on exit.
-_selector_loops = set()  # type: Set[SelectorThread]
+_selector_loops: Set["SelectorThread"] = set()
 
 
 def _atexit_callback() -> None:
@@ -88,16 +98,16 @@ class BaseAsyncIOLoop(IOLoop):
         # as windows where the default event loop does not implement these methods.
         self.selector_loop = asyncio_loop
         if hasattr(asyncio, "ProactorEventLoop") and isinstance(
-            asyncio_loop, asyncio.ProactorEventLoop  # type: ignore
+            asyncio_loop, asyncio.ProactorEventLoop
         ):
             # Ignore this line for mypy because the abstract method checker
             # doesn't understand dynamic proxies.
             self.selector_loop = AddThreadSelectorEventLoop(asyncio_loop)  # type: ignore
         # Maps fd to (fileobj, handler function) pair (as in IOLoop.add_handler)
-        self.handlers = {}  # type: Dict[int, Tuple[Union[int, _Selectable], Callable]]
+        self.handlers: Dict[int, Tuple[Union[int, _Selectable], Callable]] = {}
         # Set of fds listening for reads/writes
-        self.readers = set()  # type: Set[int]
-        self.writers = set()  # type: Set[int]
+        self.readers: Set[int] = set()
+        self.writers: Set[int] = set()
         self.closing = False
         # If an asyncio loop was closed through an asyncio interface
         # instead of IOLoop.close(), we'd never hear about it and may
@@ -419,9 +429,7 @@ class AnyThreadEventLoopPolicy(_BasePolicy):  # type: ignore
     def get_event_loop(self) -> asyncio.AbstractEventLoop:
         try:
             return super().get_event_loop()
-        except (RuntimeError, AssertionError):
-            # This was an AssertionError in Python 3.4.2 (which ships with Debian Jessie)
-            # and changed to a RuntimeError in 3.4.3.
+        except RuntimeError:
             # "There is no current event loop in thread %r"
             loop = self.new_event_loop()
             self.set_event_loop(loop)
@@ -445,11 +453,11 @@ class SelectorThread:
         self._real_loop = real_loop
 
         self._select_cond = threading.Condition()
-        self._select_args = (
-            None
-        )  # type: Optional[Tuple[List[_FileDescriptorLike], List[_FileDescriptorLike]]]
+        self._select_args: Optional[
+            Tuple[List[_FileDescriptorLike], List[_FileDescriptorLike]]
+        ] = None
         self._closing_selector = False
-        self._thread = None  # type: Optional[threading.Thread]
+        self._thread: Optional[threading.Thread] = None
         self._thread_manager_handle = self._thread_manager()
 
         async def thread_manager_anext() -> None:
@@ -464,8 +472,8 @@ class SelectorThread:
             lambda: self._real_loop.create_task(thread_manager_anext())
         )
 
-        self._readers = {}  # type: Dict[_FileDescriptorLike, Callable]
-        self._writers = {}  # type: Dict[_FileDescriptorLike, Callable]
+        self._readers: Dict[_FileDescriptorLike, Callable] = {}
+        self._writers: Dict[_FileDescriptorLike, Callable] = {}
 
         # Writing to _waker_w will wake up the selector thread, which
         # watches for _waker_r to be readable.
@@ -603,7 +611,7 @@ class SelectorThread:
                 pass
 
     def _handle_select(
-        self, rs: List["_FileDescriptorLike"], ws: List["_FileDescriptorLike"]
+        self, rs: List[_FileDescriptorLike], ws: List[_FileDescriptorLike]
     ) -> None:
         for r in rs:
             self._handle_event(r, self._readers)
@@ -613,8 +621,8 @@ class SelectorThread:
 
     def _handle_event(
         self,
-        fd: "_FileDescriptorLike",
-        cb_map: Dict["_FileDescriptorLike", Callable],
+        fd: _FileDescriptorLike,
+        cb_map: Dict[_FileDescriptorLike, Callable],
     ) -> None:
         try:
             callback = cb_map[fd]
@@ -623,18 +631,18 @@ class SelectorThread:
         callback()
 
     def add_reader(
-        self, fd: "_FileDescriptorLike", callback: Callable[..., None], *args: Any
+        self, fd: _FileDescriptorLike, callback: Callable[..., None], *args: Any
     ) -> None:
         self._readers[fd] = functools.partial(callback, *args)
         self._wake_selector()
 
     def add_writer(
-        self, fd: "_FileDescriptorLike", callback: Callable[..., None], *args: Any
+        self, fd: _FileDescriptorLike, callback: Callable[..., None], *args: Any
     ) -> None:
         self._writers[fd] = functools.partial(callback, *args)
         self._wake_selector()
 
-    def remove_reader(self, fd: "_FileDescriptorLike") -> bool:
+    def remove_reader(self, fd: _FileDescriptorLike) -> bool:
         try:
             del self._readers[fd]
         except KeyError:
@@ -642,7 +650,7 @@ class SelectorThread:
         self._wake_selector()
         return True
 
-    def remove_writer(self, fd: "_FileDescriptorLike") -> bool:
+    def remove_writer(self, fd: _FileDescriptorLike) -> bool:
         try:
             del self._writers[fd]
         except KeyError: