Function that returns a decorator to memoize stateless functions. Args: secs - Amount of time (in seconds) to keep values in the cache; the argument may be a floating point number to indicate a more precise timeout.

memoizer.py

import functools
import hashlib
import time


def memoize(secs=0):
  '''Returns a decorator to memoize stateless functions.
  Args: secs - Amount of time (in seconds) to keep values in the cache;
               The argument may be a floating point number to indicate a
               more precise timeout.
  '''

  def decorator(f):
    cache = {}

    @functools.wraps(f)
    def wrapped(*args, **kwargs):
      args_hash = hash(args)
      kwargs_keys_hash = hash(frozenset(kwargs.keys()))
      kwargs_vals_hash = hash(frozenset(kwargs.values()))

      m = hashlib.sha1()
      m.update(str(args_hash))
      m.update(str(kwargs_keys_hash))
      m.update(str(kwargs_vals_hash))
      key = m.hexdigest()

      time_now = time.time() if secs > 0 else 0

      if key not in cache:
        # store value along with expire_time in cache
        value = f(*args, **kwargs)
        cache[key] = (value, time_now + secs)

      elif secs > 0:
        # refresh cache
        expire_time = cache[key][1]
        if time_now > expire_time:
          value = f(*args, **kwargs)
          cache[key] = (value, time_now + secs)

      return cache[key][0]

    return wrapped

  return decorator