modtime.py

'''Time modulus for use with caching etc.
A time window of size window_size second distributed in chunks of granularity seconds.
'''
import time

def modtime(window_size, granularity, t=None):
  '''Time distributions
  
  modtime(60, 5)
    12 unique evenly distributed over 60 seconds
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
    Or: new token every 5th second within a 60 second rolling window.
    0 0 0 0 0 1 1 1 1 1 2 2 2 ... 10 11 11 11 11 11

  modtime(30, 3)
    10 unique numbers evenly distributed over 30 seconds.
    0, 1, 2, 3, 4, 5, 6, 7, 8, 9
    Or: new token every 3rd second within a 30 second rolling window.
    0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9
  '''
  if t is None:
    t = time.time()
  t = int(t)
  if window_size > 0:
    t -= int((t-window_size)/window_size)*window_size
  t -= t % granularity
  if window_size > 0:
    t -= window_size
  # simply return t for un-normalized values
  # return t
  if t:
    return t/granularity
  return 0

if __name__ == '__main__':
  # proof/test
  ts = time.time()
  for w, g in (
    (60, 5),
    (30, 3),
    (30, 2),
    (3600, 60),
    ):
    reg = []
    while 1:
      start = time.time()
      t = modtime(w, g, ts)
      if t not in reg:
        reg.append(t)
      if len(reg) == w/g:
        break
      ts += 1
    print w, g, reg