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Persistent caching decorator

Project description


filecache is a decorator which saves the return value of functions even after the interpreter dies. For example this is useful on functions that download and parse webpages. All you need to do is specify how long the return values should be cached (use seconds, like time.sleep).


from filecache import filecache

@filecache(24 * 60 * 60)
def time_consuming_function(args):
    # etc

def another_function(args):
    # etc

NOTE: All arguments of the decorated function and the return value need to be picklable for this to work.

NOTE: The cache isn't automatically cleaned, it is only overwritten. If your function can receive many different arguments that rarely repeat, your cache may forever grow. One day I might add a feature that once in every 100 calls scans the db for outdated stuff and erases.

NOTE: This is less useful on methods of a class because the instance (self) is cached, and if the instance isn't the same, the cache isn't used. This makes sense because class methods are affected by changes in whatever is attached to self.

Tested on python 2.7 and 3.1

License: BSD, do what you wish with this. Could be awesome to hear if you found it useful and/or you have suggestions. ubershmekel at gmail

A trick to invalidate a single value:

def somefunc(x, y, z):
    return x * y * z

del somefunc._db[filecache._args_key(somefunc, (1,2,3), {})]
# or just iterate of somefunc._db (it's a shelve, like a dict) to find the right key.

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