Counts population. Runs in the background and constantly updates the local mongo instance.

population.py

#!/usr/bin/python
from pymongo import MongoClient
import RPi.GPIO as GPIO
import threading
import time
import sys

# Using a state machine to track bee ingress/egress.
states = {
    'IDLE': 0,
    'EGRESS_1_0': 1,
    'EGRESS_1_1': 2,
    'EGRESS_0_1': 3,
    'INGRESS_0_1': 4,
    'INGRESS_1_1': 5,
    'INGRESS_1_0': 6
}

# Put all related data into one data structure. Constants are capitalized.
gates = [
    {'IN': 16, 'OUT': 18, 'state': states['IDLE']},
    {'IN': 21, 'OUT': 13, 'state': states['IDLE']},
    {'IN': 12, 'OUT': 15, 'state': states['IDLE']},
    {'IN': 29, 'OUT': 31, 'state': states['IDLE']},
    {'IN': 33, 'OUT': 35, 'state': states['IDLE']}
]

GPIO.setmode(GPIO.BOARD)

# This list comprehension puts every gate's 'IN' and 'OUT' into one big list...
pins = [x['IN'] for x in gates] + [x['OUT'] for x in gates]

# ...so we can setup every pin by just iterating over that list.
for pin in pins:
    GPIO.setup(pin, GPIO.IN)

hiveInfo = MongoClient().sensorData.hiveInfo
hI = hiveInfo.find()[0]

if 'population' in hI:
    count = hI['population']
else:
    count = 0


# This function asynchronously stores the count in Mongo every 5 seconds
def storeCount():
    hiveInfo.update({}, {'$set': {'population': count}})
    threading.Timer(5, storeCount).start()


storeCount()

# Event loop. Cheap asynchronous behaviour, hence the state machine.
while True:
    for gate in gates:
        inSensor = not GPIO.input(gate['IN'])  # Compensating for active low
        outSensor = not GPIO.input(gate['OUT'])

        # State machine logic.
        if gate['state'] is states['IDLE']:
            if inSensor:
                gate['state'] = states['EGRESS_1_0']

            elif outSensor:
                gate['state'] = states['INGRESS_0_1']

        elif gate['state'] is states['EGRESS_1_0']:
            if outSensor:
                gate['state'] = states['EGRESS_1_1']

            elif not inSensor:
                gate['state'] = states['IDLE']

        elif gate['state'] is states['EGRESS_1_1']:
            if not inSensor:
                gate['state'] = states['EGRESS_0_1']

            elif not outSensor:
                gate['state'] = states['EGRESS_1_0']

        elif gate['state'] is states['EGRESS_0_1']:
            if inSensor:
                gate['state'] = states['EGRESS_1_1']

            elif not outSensor:
                gate['state'] = states['IDLE']

                count += 1 # A bee has entered the hive.
                sys.stdout.write('\r%s        ' % repr(count))

        elif gate['state'] is states['INGRESS_0_1']:
            if inSensor:
                gate['state'] = states['INGRESS_1_1']

            elif not outSensor:
                gate['state'] = states['IDLE']

        elif gate['state'] is states['INGRESS_1_1']:
            if not outSensor:
                gate['state'] = states['INGRESS_1_0']

            elif not inSensor:
                gate['state'] = states['INGRESS_0_1']

        elif gate['state'] is states['INGRESS_1_0']:
            if outSensor:
                gate['state'] = states['INGRESS_1_1']

            elif not inSensor:
                gate['state'] = states['IDLE']

                if count > 0: # No (arithmetically) negative bees. 
                    count -= 1 # A bee has exited the hive.
                    sys.stdout.write('\r%s        ' % repr(count))

    time.sleep(0.01)