Fix type annotations

adafruit_pcf8591/analog_in.py

@@ -29,19 +29,20 @@
 
 try:
     import typing  # pylint: disable=unused-import
-    from adafruit_pcf8591.pcf8591.PCF8591 import PCF8591
+    from typing_extensions import Literal
+    from adafruit_pcf8591.pcf8591 import PCF8591
 except ImportError:
     pass
 
 
 class AnalogIn:
     """AnalogIn Mock Implementation for ADC Reads."""
 
-    def __init__(self, pcf: PCF8591, pin: int) -> None:
+    def __init__(self, pcf: PCF8591, pin: Literal[0, 1, 2, 3]) -> None:
         """AnalogIn
 
         :param pcf: The PCF8591 object.
-        :param int pin: Required ADC channel pin.
+        :param int pin: Required ADC channel pin; must be 0-3 inclusive
 
         """
         self._pcf = pcf

adafruit_pcf8591/analog_out.py

@@ -28,19 +28,20 @@
 """
 try:
     import typing  # pylint: disable=unused-import
-    from adafruit_pcf8591.pcf8591.PCF8591 import PCF8591
+    from typing_extensions import Literal
+    from adafruit_pcf8591.pcf8591 import PCF8591
 except ImportError:
     pass
 
 
 class AnalogOut:
     """AnalogIn Mock Implementation for ADC Reads."""
 
-    def __init__(self, pcf: PCF8591, dac_pin: int = 0) -> None:
+    def __init__(self, pcf: PCF8591, dac_pin: Literal[0] = 0) -> None:
         """AnalogIn
 
         :param pcf: The pcf object.
-        :param int pin: Required pin must be adafruit_pcf8591.pcf8591.A0
+        :param int dac_pin: Required pin must be adafruit_pcf8591.pcf8591.A0
 
         """
         self._pcf = pcf

adafruit_pcf8591/pcf8591.py

@@ -97,7 +97,7 @@ def _half_read(self, channel: Literal[0, 1, 2, 3]) -> None:
         with self.i2c_device as i2c:
             i2c.write_then_readinto(self._buffer, self._buffer)
 
-    def read(self, channel: Literal[0, 1, 2, 3]) -> None:
+    def read(self, channel: Literal[0, 1, 2, 3]) -> int:
         """Read an analog value from one of the four ADC inputs
 
         :param int channel: The single-ended ADC channel to read from, 0 thru 3