Time based cache decorator

cache.py

import functools
import logging
import time


logger = logging.getLogger(__name__)
MAX_ENTRIES = 100  # Max items per cache!


def memoize(expire_seconds):
    """Time-Expiration based cache decorator.

    Arguments to the cached function must be hashable.
    Clear the cache using f.cache_clear().
    Debug the interval cache using f.get_cache().
    """
    placeholder = object()

    def decorating(func):
        cache = {}

        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            key = functools._make_key(args, kwargs, False)
            cache_info = cache.get(key, placeholder)
            if cache_info is not placeholder:
                # Cache Hit!
                now = time.monotonic()
                if now <= cache_info[0]:
                    # Cache still valid
                    logger.debug('Cache found %s for %s', key, func.__name__)
                    return cache_info[1]
                else:
                    # Try to make room cleaning this key
                    logger.debug('Cache expired %s for %s', key, func.__name__)
                    try:
                        del cache[key]
                    except KeyError:
                        # Other thread could have deleted the key
                        pass

            result = func(*args, **kwargs)
            # If we have room save the result
            if len(cache) < MAX_ENTRIES:
                logger.debug('Cache saving key %s for %s result %s', key, func.__name__, result)
                expiration = time.monotonic() + expire_seconds
                cache[key] = (expiration, result)
            return result

        def clear_cache():
            """Clean the interval cache of the user function."""
            cache.clear()

        def get_cache():
            """Return the interval cache (useful for debugging)."""
            return cache

        # Public API to manipulate the cache from outside
        wrapper.clear_cache = clear_cache
        wrapper.get_cache = get_cache
        return wrapper

    return decorating