Add abstract classes and Final to type hinting.

src/abstract.py

+from abc import ABC, abstractmethod
+
+
+class ProximitySensor(ABC):
+    """Abstract proximity sensor."""
+
+    @property
+    @abstractmethod
+    def proximity(self) -> int:
+        ...
+
+
+class LEDController(ABC):
+    """Abstract LED controller."""
+
+    @abstractmethod
+    def fill(self, color: tuple[int, int, int]) -> None:
+        ...
+
+
+class TouchSensor(ABC):
+    """Abstract touch sensor."""
+
+    @property
+    @abstractmethod
+    def value(self) -> bool:
+        ...

src/interact.py

+from .abstract import LEDController, ProximitySensor, TouchSensor
 from .pulse import run_simple_pulse
 from .prox_pulse import run_prox_pulse
 from .morse_engine import run_morse_engine
 
 
-def run(apds, pixels, touch):
+def run(apds: ProximitySensor, pixels: LEDController, touch: TouchSensor):
     """
     Runs the selected demo on the Trinkey.
 

src/morse_code.py

 from .symbols import MORSE_SYMBOL_TO_LETTER, InvalidSymbolError
 
 
-def append_morse_symbol(message, symbol):
+def append_morse_symbol(message: str, symbol: str) -> str:
     """
     Decodes a Morse code symbol and appends the corresponding character to the 
     message.
@@ -21,7 +21,7 @@ def append_morse_symbol(message, symbol):
     raise InvalidSymbolError()
 
 
-def translate_message(morse):
+def translate_message(morse: str) -> str:
     """
     Translates a Morse code message into an English string.
 

src/morse_engine.py

 import time
+from typing import Final
+
 from src import morse_code
+from .abstract import LEDController, TouchSensor, ProximitySensor
 
 # Constants (Keep same or tests will break)
-THRESHOLD = 75
-UNIT_TIME = 0.24
+THRESHOLD: Final[int] = 75
+UNIT_TIME: Final[float] = 0.24
 
-RED = (255, 0, 0)
-YELLOW = (220, 160, 0)
-GREEN = (0, 255, 0)
+RED   : Final[tuple[int, int, int]] = (255, 0,   0)
+YELLOW: Final[tuple[int, int, int]] = (220, 160, 0)
+GREEN : Final[tuple[int, int, int]] = (0,   255, 0)
 
 # Legacy ham radio license requirement
 # - 0.24 sec unit time (5 words per minute)
@@ -15,7 +18,7 @@ GREEN = (0, 255, 0)
 # - 0.034 sec unit time (35 words per minute)
 
 
-def set_color(elapsed_t, px):
+def set_color(elapsed_t: float, px: LEDController):
     """
     Lights the LEDs on the trinkey depending on the length of input.
     
@@ -26,7 +29,7 @@ def set_color(elapsed_t, px):
     pass
 
 
-def add_mark(elapsed_t):
+def add_mark(elapsed_t: float) -> str:
     """
     Determines if input is a dot (.), dash (-), or nothing ("") based 
     on the length of input.
@@ -40,7 +43,7 @@ def add_mark(elapsed_t):
     pass
 
 
-def run_morse_engine(apds, pixels, touch):
+def run_morse_engine(apds: ProximitySensor, pixels: LEDController, touch: TouchSensor):
     """
     Runs Morse code translation based on proximity input.
 

src/prox_pulse.py

 import time
 from .pulse import pulse
+from .abstract import LEDController, ProximitySensor
 
 THRESHOLD = 75
 
@@ -7,7 +8,7 @@ RED = (150, 10, 10)
 GREEN = (30, 100, 10)
 
 
-def prox_pulse(px, color, prox):
+def prox_pulse(px: LEDController, color: tuple[int, int, int], prox: int) -> None:
     """
     Maps proximity value to pulse duration and calls pulse.
 
@@ -19,7 +20,7 @@ def prox_pulse(px, color, prox):
     pass  # Delete this line when you start coding!
 
 
-def run_prox_pulse(apds, pixels):
+def run_prox_pulse(apds: ProximitySensor, pixels: LEDController) -> None:
     """
     Runs proximity-based pulsing demo.
 

src/pulse.py

 import time
+from typing import Final
 
-THRESHOLD = 75
-BLUE = (0, 0, 255)
-TIME = 1
+from .abstract import LEDController
 
+THRESHOLD: Final[int] = 75
+BLUE: Final[tuple[int, int, int]] = (0, 0, 255)
+TIME: Final[int] = 1
 
-def pulse(px, color, duration):
+
+def pulse(px: LEDController, color: tuple[int, int, int], duration: float):
     """
     Fills pixels with a color for a duration, then turns them off.
 
@@ -17,7 +20,7 @@ def pulse(px, color, duration):
     pass  # Delete this line when you start coding!
 
 
-def run_simple_pulse(pixels):
+def run_simple_pulse(pixels: LEDController):
     """
     Runs a simple pulse demo.
 

src/symbols.py

-MORSE_SYMBOL_TO_LETTER = {
+from typing import Final
+
+MORSE_SYMBOL_TO_LETTER: Final[dict[str, str]] = {
     ".-": "A",
     "-...": "B",
     "-.-.": "C",