Prevent subclassing of the Robot object (#21)

Author: RealOrangeOne

sr/robot3/robot.py

@@ -8,7 +8,7 @@
 from pathlib import Path
 from socket import socket
 from types import MappingProxyType
-from typing import Mapping, Optional
+from typing import Mapping, Optional, final
 
 from . import game_specific, timeout
 from ._version import __version__
@@ -23,12 +23,15 @@
 from .raw_serial import RawSerial
 from .servo_board import ServoBoard
 from .simulator.time_server import TimeServer
-from .utils import IN_SIMULATOR, ensure_atexit_on_term, obtain_lock, singular
+from .utils import (
+    IN_SIMULATOR, FinalMeta, ensure_atexit_on_term, obtain_lock, singular,
+)
 
 logger = logging.getLogger(__name__)
 
 
-class Robot:
+@final
+class Robot(metaclass=FinalMeta):
     """
     The main robot class that provides access to all the boards.
 

sr/robot3/utils.py

@@ -7,7 +7,7 @@
 import socket
 from abc import ABC, abstractmethod
 from types import FrameType
-from typing import Any, Mapping, NamedTuple, Optional, TypeVar
+from typing import Any, Mapping, NamedTuple, Optional, Type, TypeVar
 
 from serial.tools.list_ports import comports
 from serial.tools.list_ports_common import ListPortInfo
@@ -77,6 +77,18 @@ def identify(self) -> BoardIdentity:
         pass  # pragma: no cover
 
 
+class FinalMeta(type):
+    """
+    A meta class which ensures a given class cannot be subclassed.
+
+    It's recommended to additionally use typing.final.
+    """
+    def __new__(cls, name: str, bases: tuple, classdict: dict) -> Type:
+        if bases:
+            raise TypeError(f"{name} cannot be sub-classed.")
+        return super().__new__(cls, name, bases, dict(classdict))
+
+
 def map_to_int(
         x: float,
         in_min: float,

tests/test_sr_robot.py

@@ -139,3 +139,9 @@ def test_robot_discovery() -> None:
     assert robot.power_board == robot.boards[power_asset_tag]
     assert robot.servo_board == robot.boards[servo_asset_tag]
     assert robot.motor_board == robot.boards[motor_asset_tag]
+
+
+def test_cannot_subclass() -> None:
+    with pytest.raises(TypeError, match="Robot cannot be sub-classed"):
+        class MyRobot(Robot):
+            pass