I have created a decorator memoization class that I am actively using for cache my calls. There are already many excellent suggestions on how to implement python memoization.
The class that I have created currently uses get and set method calls to set the cacheTimeOut. They are called getCacheTimeOut()
and setCacheTimeOut()
. While this is an adequate solution. I was hoping to use the @property
and @cacheTimeOut.setter
decorators to enable the functions to be called directly as for example cacheTimeOut=120
The problem is in the details. I do not know how to make these properties accessible in the __get__
method. The __get__
method assigns the different function calls defined within the class to functions.partial.
Here is my script example designed for Python 2.7
import time
from functools import partial
import cPickle
class memoize(object):
def __init__(self, func):
self.func = func
self._cache = {}
self._timestamps = {}
self._cacheTimeOut = 120
self.objtype = None
def __new__(cls, *args, **kwargs):
return object.__new__(cls,*args, **kwargs)
def __get__(self, obj, objtype=None):
"""Used for object methods where decorator has been placed before methods."""
self.objtype = objtype
fn = partial(self, obj)
fn.resetCache = self.resetCache
fn.getTimeStamps = self.getTimeStamps
fn.getCache = self.getCache
fn._timestamps = self._timestamps
fn.setCacheTimeOut = self.setCacheTimeOut
fn.getCacheTimeOut = self.getCacheTimeOut
return fn
def __argsToKey(self, *args, **kwargs):
args = list(args)
for x, arg in enumerate(args): # remove instance from
if self.objtype:
if isinstance(arg, self.objtype):
args.remove(arg)
str = cPickle.dumps(args, 1)+cPickle.dumps(kwargs, 1)
return str
def __call__(self, *args, **kwargs):
"""Main calling function of decorator."""
key = self.__argsToKey(*args, **kwargs)
now = time.time() # get current time to query for key
if self._timestamps.get(key, now) > now:
return self._cache[key]
else:
value = self.func(*args, **kwargs)
self._cache[key] = value
self._timestamps[key] = now + self._cacheTimeOut
return value
def __repr__(self):
'''Return the function's docstring.'''
return self.func.__doc__
def resetCache(self):
"""Resets the cache. Currently called manually upon request."""
self._cache = {}
self._timestamps = {}
def getCacheTimeOut(self):
"""Get the cache time out used to track stale data."""
return self._cacheTimeOut
def setCacheTimeOut(self, timeOut):
"""Set the cache timeout to some other value besides 120. Requires an integer value. If you set timeOut to zero you are ignoring the cache"""
self._cacheTimeOut = timeOut
def getCache(self):
"""Returns the cache dictionary."""
return self._cache
def getTimeStamps(self):
"""Returns the encapsulated timestamp dictionary."""
return self._timestamps
@property
def cacheTimeOut(self):
"""Get cacheTimeOut."""
return self._cacheTimeOut
@cacheTimeOut.setter
def cacheTimeOut(self, timeOut):
"""Set cacheTimeOut."""
self._cacheTimeOut = timeOut
memoize
def increment(x):
increment.count+=1
print("increment.count:%d, x:%d"%(increment.count, x))
x+=1
return x
increment.count = 0 # Define the count to track whether calls to increment vs cache
class basic(object):
def __init__(self):
self.count = 0
@memoize
def increment(self, x):
self.count+=1
print("increment.count:%d, x:%d"%(increment.count, x))
x+=1
return x
def main():
print increment(3)
print increment(3)
# What I am actually doing
print increment.getCacheTimeOut() # print out default of 120
increment.setCacheTimeOut(20) # set to 20
print increment.getCacheTimeOut() # verify that is has been set to 120
# What I would like to do and currently does not work
print increment.cacheTimeOut
# Assign to property
increment.cacheTimeOut = 20
myObject = basic()
print myObject.increment(3)
print myObject.count
print myObject.increment(3)
print myObject.count
print myObject.increment(4)
print myObject.count
####### Unittest code.
import sys
import time
import unittest
from memoize import memoize
class testSampleUsages(unittest.TestCase):
# """This series of unit tests is to show the user how to apply memoize calls."""
def testSimpleUsageMemoize(self):
@memoize
def increment(var=0):
var += 1
return var
increment(3)
increment(3)
def testMethodBasedUsage(self):
"""Add the @memoize before method call."""
class myClass(object):
@memoize
def increment(self,var=0):
var += 1
return var
@memoize
def decrement(self, var=0):
var -=1
return var
myObj = myClass()
myObj.increment(3)
myObj.increment(3)
myObj.decrement(6)
myObj.decrement(6)
def testMultipleInstances(self):
@memoize
class myClass(object):
def __init__(self):
self.incrementCountCalls = 0
self.decrementCountCalls = 0
self.powCountCall = 0
# @memoize
def increment(self,var=0):
var += 1
self.incrementCountCalls+=1
return var
# @memoize
def decrement(self, var=0):
self.decrementCountCalls+=1
var -=1
return var
def pow(self, var=0):
self.powCountCall+=1
return var*var
obj1 = myClass() # Memoizing class above does not seem to work.
obj2 = myClass()
obj3 = myClass()
obj1.increment(3)
obj1.increment(3)
#obj2.increment(3)
#obj2.increment(3)
#obj3.increment(3)
#obj3.increment(3)
obj1.pow(4)
obj2.pow(4)
obj3.pow(4)
There's no way to attach a property
to a single instance. Being descriptors, property
s must be part of a class definition in order to function. That means you can't easily add them to the partial
object you create in __get__
.
Now, you could create a class of your own to reimplement the behavior of partial
with your added property. However, I suspect the limitation is actually to your benefit. If memo
is applied to a method, its state is shared by all instances of the class (and perhaps even instances of subclasses). If you allow the caching details to be adjusted through instances, you might confuse users with cases like:
obj1 = basic()
print obj1.increment.getCacheTimeout() # prints the initial value, e.g. 120
obj2 = basic()
obj2.increment.setCacheTimeOut(20) # change the timeout value via another instance
print obj1.increment.getCacheTimeout() # the value via the first instance now prints 20
I suggest that you make the memoization-related interfaces of decorated methods accessible only through the class, not through instances. To make that work, you need to update your __get__
method to work if obj
is None
. It can simply return self
:
def __get__(self, obj, objtype=None):
if obj is None:
return self
self.objtype = objtype
return partial(self, obj) # no need to attach our methods to the partial anymore
With this change, using a property
on the memo
via the class works:
basic.increment.cacheTimeOut = 20 # set property of the "unbound" method basic.increment
There is actually a way to accomplish this - by rebinding the decorator as instance-object with a call -method
class Helper(object):
def __init__(self, d, obj):
self.d = d
self.obj = obj
self.timeout = 0
def __call__(self, *args, **kwargs):
print self, self.timeout
return self.d.func(self.obj, *args, **kwargs)
class decorator(object):
def __init__(self, func):
self.func = func
self.name = func.__name__
def __get__(self, obj, clazz):
if object is not None:
obj.__dict__[self.name] = Helper(self, obj)
return obj.__dict__[self.name]
class Foo(object):
@decorator
def bar(self, args):
return args * 2
f = Foo()
g = Foo()
f.bar.timeout = 10
g.bar.timeout = 20
print f.bar(10)
print g.bar(20)
HTH
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