SlidingCounter.py

import bisect, time


#this module makes use of the bisect module, especially bisect.bisect_left().
#see https://docs.python.org/2/library/bisect.html for details.

class SlidingCounter(object):

	def __init__(self):
		self.event_arr = []
		self.num_events = 0

	def get_millis_now(self):
		return int(time.time() * 1000)

	def clear_old_event_arr(self):
		two_hr_ago = self.get_millis_now() - 1000 * 60 * 60 * 2
		#if the array's oldest element is older than 2 hours, find the position where the 2h mark could be inserted in the array, and slice the event array forward from this point
		if(self.num_events and (self.event_arr[0] < two_hr_ago)): 
			self.event_arr = self.event_arr[bisect.bisect_left(self.event_arr,two_hr_ago):]
			self.num_events = len(self.event_arr)

	def increment(self):
		self.clear_old_event_arr() # if its been more than two hours, then old events get flushed from the array
		self.event_arr.append(self.get_millis_now())
		self.num_events = self.num_events + 1

	#here, like in all num*() functions, we subtract the number of total events from those that are older than the 1 second mark
	def numLastSecond(self):
		sec_threshold = self.get_millis_now() - 1000
		return self.num_events - bisect.bisect_left(self.event_arr, sec_threshold)

	def numLastMinute(self):
		sec_threshold = self.get_millis_now() - 1000 * 60
		return self.num_events - bisect.bisect_left(self.event_arr, sec_threshold)

	def numLastHour(self):
		sec_threshold = self.get_millis_now() - 1000 * 60 * 60
		return self.num_events - bisect.bisect_left(self.event_arr, sec_threshold)

	#added this function for testing pursposes
	def numLastTenSeconds(self):
		sec_threshold = self.get_millis_now() - 10000
		return self.num_events - bisect.bisect_left(self.event_arr, sec_threshold)


#we have testing code in the main function
if __name__ == "__main__":
	sc = SlidingCounter()
	print "init count, last second (0), last 10 seconds (0): ",sc.numLastSecond()," ",sc.numLastTenSeconds()
	ctr = 0
	while ctr < 60:
		sc.increment()
		ctr = ctr + 1
	print "immediate count, last second (60), last 10 seconds (60): ",sc.numLastSecond()," ",sc.numLastTenSeconds()
	time.sleep(1)
	print "1 sec delay before append, last second (0), last 10 seconds(60): ",sc.numLastSecond()," ",sc.numLastTenSeconds()

	ctr = 0
	while ctr < 20:
		sc.increment()
		ctr = ctr + 1

	print "1 sec delay after append, last second (20), last 10 seconds(80): ",sc.numLastSecond()," ",sc.numLastTenSeconds()

	time.sleep(9)
	print "10 sec delay, last second (0), last 10 seconds(20): ",sc.numLastSecond()," ",sc.numLastTenSeconds()