Code cleanup for /u/SquidgeyBear. (See thread at http://redd.it/3tpv6v, and comment at https://goo.gl/G2H67c)

traffic_light_simulation.py

#!/usr/bin/env python3
"""
Runs a simulation of a traffic light cycle.

Written by /u/masasin as code cleanup for /u/SquidgeyBear. See the original
thread at https://redd.it/3tpv6v, and the explanatory comments at
https://goo.gl/G2H67c.

"""
from itertools import cycle
import logging
import time

import RPi.GPIO as GPIO


# Light colours and pin numbers.
lights = {"green": 29,
          "amber": 31,
          "red": 33}


def initialize():
    """Set up GPIO and turn on the output pins."""
    GPIO.setmode(GPIO.BOARD)  # Use physical pin numbers.

    logging.debug("Initializing GPIO pins")
    for colour, pin in lights.items():
        logging.debug("Setting {colour} (pin {pin}) to output"
                      .format(colour=colour, pin=pin))
        GPIO.setup(pin, GPIO.out)


def handle_led(colour, state):
    """
    Turn a coloured LED on or off.

    Parameters
    ----------
    colour : str
        The colour of the LED.
    state : bool
        Whether the LED should be on or OFF.

    """
    logging.debug("{colour} {state}".format(colour=colour.capitalize(),
                                            state="on" if state else "off"))
    GPIO.output(lights[colour], state)


def set_lights(config):
    """
    Set all the LEDs to a specific configuration.

    Parameters
    ----------
    config : str
        The colours that need to be on, separated by a space.

    """
    for colour in lights:
        if colour in config.split():  # Split at the space and check.
            handle_led(colour, True)
        else:
            handle_led(colour, False)


def main():
    """Main entry point for the script."""
    logging.info("Started traffic light simulation")

    configurations = ["green", "amber", "red", "amber red"]
    main_clock, current_config = 0
    pedestrian_waiting = False
    sleep_duration = 0.5  # seconds

    try:
        initialize()  # Note that it's inside the try-except-finally block.

	for configuration in cycle(configurations):
            set_lights(configuration)

            if not pedestrian_waiting:
                if main_clock % 5 == 0:  # Every five ticks (2.5 seconds)
                    continue
            else:
                logging.debug("There is a pedestrian!")

            main_clock += 1
            time.sleep(sleep_duration)

    except KeyboardInterrupt:  # Exit cleanly by pressing Ctrl+C.
        logging.info("Exiting simulation")

    finally:
        GPIO.cleanup()


if __name__ == "__main__":
    logging.basicConfig(level=logging.INFO)  # logging.DEBUG gives more info.
    main()