fix some typing errors

.flake8

@@ -0,0 +1,2 @@
+[flake8]
+max-line-length = 100

megacom/__init__.py

@@ -1,13 +1,13 @@
 import argparse
 import asyncio
 import contextlib
-import os
 import re
 import sys
 import termios
 import tty
 from types import TracebackType
-from typing import Optional, Tuple, Type
+from typing import Any, List, Optional, Tuple, Type
+from typing_extensions import Literal
 
 import serial
 import serial_asyncio
@@ -30,11 +30,14 @@ MODE_LOOKUP = {
 
 class TtyRaw:
     __slots__ = ["isatty", "fd", "settings"]
+    isatty: bool
+    fd: int
+    settings: List[Any]
 
     def __init__(self) -> None:
         self.isatty = False
-        self.fd = None
-        self.settings = None
+        self.fd = 0
+        self.settings = []
 
     def __enter__(self) -> None:
         if sys.stdin.isatty():
@@ -46,9 +49,10 @@ class TtyRaw:
 
     def __exit__(self, exc_type: Optional[Type[BaseException]],
                  exc_value: Optional[BaseException],
-                 exc_traceback: Optional[TracebackType]) -> bool:
+                 exc_traceback: Optional[TracebackType]) -> Literal[False]:
         if self.isatty:
             termios.tcsetattr(self.fd, termios.TCSADRAIN, self.settings)
+        return False
 
 
 async def setup_async() -> Tuple[asyncio.StreamReader, asyncio.StreamWriter]: