import types
def cachedmethod(function):
return types.MethodType(Memoize(function), None)
class Memoize:
def __init__(self,function):
self._cache = {}
self._callable = function
def __call__(self, *args, **kwds):
cache = self._cache
key = self._getKey(*args,**kwds)
try: return cache[key]
except KeyError:
cachedValue = cache[key] = self._callable(*args,**kwds)
return cachedValue
def _getKey(self,*args,**kwds):
return kwds and (args, ImmutableDict(kwds)) or args
class ImmutableDict(dict):
'''A hashable dict.'''
def __init__(self,*args,**kwds):
dict.__init__(self,*args,**kwds)
def __setitem__(self,key,value):
raise NotImplementedError, "dict is immutable"
def __delitem__(self,key):
raise NotImplementedError, "dict is immutable"
def clear(self):
raise NotImplementedError, "dict is immutable"
def setdefault(self,k,default=None):
raise NotImplementedError, "dict is immutable"
def popitem(self):
raise NotImplementedError, "dict is immutable"
def update(self,other):
raise NotImplementedError, "dict is immutable"
def __hash__(self):
return hash(tuple(self.iteritems()))
if __name__ == '__main__':
from math import sqrt,log,sin,cos
class Example:
def __init__(self,x,y):
# self._x and self._y should not be changed after initialization
self._x = x
self._y = y
@cachedmethod
def computeSomething(self, alpha, beta):
w = log(alpha) * sqrt(self._x * alpha + self._y * beta)
z = log(beta) * sqrt(self._x * beta + self._y * alpha)
return sin(z) / cos(w)
