@@ -10,7 +10,7 @@ """Various caching utilites. """ -__all__ = ["memoize", "clear_cache", "TimedDict", "MintCache"] +__all__ = ["memoize", "clear_cache", "SizedDict", "DictCache", "MintCache"] import time import math @@ -24,8 +24,23 @@ local_cache = {'__created__': (time.ctime(), 0)} def clear_cache(): """Clear out the module cache""" local_cache.clear() - -class TimedDict(object): + +class SizedDict(dict): + ''' A dictionary with a limit of items. ''' + + def __init__(self, size=1000): + dict.__init__(self) + self._maxsize = size + self._stack = [] + + def __setitem__(self, name, value): + if len(self._stack) >= self._maxsize: + self.__delitem__(self._stack[0]) + del self._stack[0] + self._stack.append(name) + return dict.__setitem__(self, name, value) + +class DictCache(object): """A wrapper around a dictionary to provide time-based expiration. This is intended to be used as a module cache on App Engine.""" def __init__(self, storage=local_cache): @@ -80,10 +95,10 @@ class MintCache(object): http://www.djangosnippets.org/snippets/793/ http://www.djangosnippets.org/snippets/155/ """ - def __init__(self, storage=TimedDict(), delay=DEFAULT_DELAY): + def __init__(self, storage=DictCache(), delay=DEFAULT_DELAY): """Create a wrapper Args: - storage: a cache backend. By default, it uses TimedDict + storage: a cache backend. By default, it uses DictCache and compatible with Google App Engine memcache API. delay: the amount of delay (in seconds) after the timeout happens @@ -115,7 +130,7 @@ class MintCache(object): packed_val = (val, timeout, refreshed) return self.storage.set(key, packed_val, real_timeout) -def memoize(key_func=None, storage=TimedDict(), age=0): +def memoize(key_func=None, backend=DictCache(), age=0): """Caches the result of a function in a cache backend. Args: @@ -123,7 +138,7 @@ def memoize(key_func=None, storage=TimedDict(), age=0): If this is a string, this string is used as format for the key. If this is None, the key is built using combination of module name, function name and all of the arguments. - storage: a cache backend. By default, it uses TimedDict but it + backend: a cache backend. By default, it uses DictCache but it is compatible with Google App Engine memcache API. age: number of seconds to keep values in cache @@ -145,19 +160,19 @@ def memoize(key_func=None, storage=TimedDict(), age=0): from google.appengine.api import memcache - @memoize(key_func='account:name=%s', storage=memcache.Client(), age=30) + @memoize(key_func='account:name=%s', backend=memcache.Client(), age=30) def get_account_by_name(name): return Account.all().filter('name =', name).get() To avoid dogpile effect using module cache: - @memoize(key_func='account:name=%s', storage=MintCache()) + @memoize(key_func='account:name=%s', backend=MintCache()) def get_account_by_name(name): return Account.all().filter('name =', name).get() To avoid dogpile effect using memcache: - @memoize(key_func='account:name=%s', storage=MintCache(memcache.Client())) + @memoize(key_func='account:name=%s', backend=MintCache(memcache.Client())) def get_account_by_name(name): return Account.all().filter('name =', name).get() @@ -181,7 +196,7 @@ def memoize(key_func=None, storage=TimedDict(), age=0): def __memoize(*args, **kwargs): try: key = key_func(func, *args, **kwargs) - value = storage.get(key) + value = backend.get(key) if value is None: value = func(*args, **kwargs) if value is not None: @@ -189,7 +204,7 @@ def memoize(key_func=None, storage=TimedDict(), age=0): timeout = 0 else: timeout = time.time() + age - storage.set(key, value, timeout) + backend.set(key, value, timeout) return value except TypeError, exc: # uncachable -- for instance, passing a list as an argument. @@ -198,8 +213,20 @@ def memoize(key_func=None, storage=TimedDict(), age=0): return __memoize return _memoize - +def run_tests(): + def test_sized_dict(): + h = SizedDict(1) + for c in ['a', 'b', 'c']: + h[c] = c + assert h[c] == c + + assert len(h) == 1 + + test_sized_dict() + if __name__ == '__main__': + run_tests() + @memoize() def fib(n): if n in (0, 1): @@ -223,4 +250,5 @@ if __name__ == '__main__': cProfile.run('print fibConstant(30)') print local_cache assert fib(10) == fibFormat(10) - assert fib(10) == fibConstant(10) + assert fib(10) == fibConstant(10) + pquest/cache.py 6151053949bc7af13eeeadce5a8a223ab421f0ad Cuong Tran ctran@pragmaquest.com http://github.com/ctran/pquest-py/commit/a73ed89ff083633cd45272a608c7e908292a0503 a73ed89ff083633cd45272a608c7e908292a0503 2009-05-07T12:53:15-07:00 2009-05-07T12:53:15-07:00 added a fixed-size dict 42675f35b1d662f65e054128ea1c7c23c9b4434b Cuong Tran ctran@pragmaquest.com