import time
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)

GPIO.setup(26, GPIO.IN, pull_up_down = GPIO.PUD_DOWN)

i = 0

start = time.time()

while time.time() - start < 60: # sample for 1 minute
        GPIO.wait_for_edge(26, GPIO.FALLING)
        i += 1

# 10000 impulses per hour @ 1kW
# =  10 impulses per hour @ 1W
# i = watts * 10 / hours
# 1 minute = 1/60 hours
# i = watts * 10 / (1/60)

watts = i * 60.0 / 10.0

print watts, "Watts"

GPIO.cleanup()