python function cache

1# Example use - Decorator code below -----------------------------
2import time
3
4@cache(ttl=timedelta(minutes=3), max_entries=300)
5def add(a, b):
6    time.sleep(2)
7    return a + b
8
9@cache()
10def substract(a, b):
11    time.sleep(2)
12    return a - b
13  
14  
15# Decorator code -----------------------------
16from datetime import datetime, timedelta
17
18def cache(**kwargs):
19  def decorator(function):
20    # static function variable for cache, lazy initialization
21    try: function.cache
22    except: function.cache = {}
23    def wrapper(*args):
24        # if nothing valid in cache, insert something
25        if not args in function.cache or datetime.now() > function.cache[args]['expiry']:
26            if 'max_entries' in kwargs:
27                max_entries = kwargs['max_entries']
28                if max_entries != None and len(function.cache) >= max_entries:
29                    now = datetime.now()
30                    function.cache = { key: function.cache[key] for key in function.cache.keys() if function.cache[key]['expiry'] > now }
31                    # if nothing is expired that is deletable, delete the first
32                    if len(function.cache) >= max_entries:
33                        del function.cache[next(iter(function.cache))]
34            function.cache[args] = {'result': function(*args), 'expiry': datetime.max if 'ttl' not in kwargs else datetime.now() + kwargs['ttl']}
35
36        # answer from cache
37        return function.cache[args]['result']
38    return wrapper
39  return decorator
40