Simple Persistence Caching: make a function cached to disk with a simple decorator.

spc.py

#!/usr/bin/env python
# Koen Bollen <meneer koenbollen nl>
# 2010 GPL
#
# Simple Persistence Caching
#

import os
import shelve
import urllib2
from functools import wraps
from time import time
import struct

__all__ = [ "cached", "download" ]

def cached( f=None, expire=None ):
    if f is None:
        cached.expire = expire
        return cached
    c = shelve.open( "/tmp/cache-%s-%s"%(os.getlogin(),f.__name__), 'c', -1 )
    @wraps(f)
    def wrapper( *args, **kwargs ):
        h = struct.pack( "l", hash( args+tuple(kwargs.items()) ) )
        try:
            result, created = c[h]
            if cached.expire and time()-created > cached.expire:
                raise KeyError
        except KeyError:
            result = f( *args, **kwargs )
            c[h] = result, time()
        except TypeError:
            result = f( *args, **kwargs )
        return result
    return wrapper
cached.expire = None

@cached( expire=300 )
def download( url, fp=None ):
    res = urllib2.urlopen( url )
    try:
        if fp is not None:
            while True:
                chunk = res.read( 4096 )
                if not chunk:
                    break
                fp.write( chunk )
            return
        data = res.read()
        return data
    finally:
        res.close()

@cached
def add5( x ):
    from time import sleep
    sleep(1)
    return x+5

def test():
    print add5( 5 )
    print add5( x=5 )

if __name__ == "__main__":
    test()

# vim: expandtab shiftwidth=4 softtabstop=4 textwidth=79:

You need to set os.environ['PYTHONHASHSEED'] = 0 or hash will be different on each session.

You need to set os.environ['PYTHONHASHSEED'] = 0 or hash will be different on each session.

Good to know! 👍 But this code snippet is from 13 years ago... 😁 But I learned something new about Python! Cheers!