Python调用函数时用** kwargs记忆似乎不起作用

Question

The call to GetData1 works well and prints:

hello 67 8.3

the call to GetData2 fails:

TypeError: __call__() got an unexpected keyword argument 'arg1'

My code is

class Memoized(object):
    def __init__(self, func):
        self.func = func
        self.cache = {}

    def __call__(self, *args):
        print args
        with Locker:
            try:
                return self.cache[args]
            except KeyError:
                self.cache[args] = value = self.func(*args)
                return value


def GetData1(arg1, arg2, arg3) :
    print arg1, arg2, arg3

@Memoized
def GetData2(arg1, arg2, arg3) :
    print arg1, arg2, arg3



r = { 'arg1' : 'hello', 'arg2': 67, 'arg3' : 8.3 }
GetData1(**r)
GetData2(**r)

Answer 1

Your @Memoized class replaces (wraps) the GetData2() function and shadows it with itself, being a callable which takes *args , but no **kwargs .

A possible solution could be

def __call__(self, *args, **kwargs):
    print args
    with Locker:
        kwitems = tuple(sorted(kwargs.items()))
        try:
            return self.cache[args, kwitems]
        except KeyError:
            self.cache[args, kwitems] = value = self.func(*args)
            return value

But then it makes a difference for the cache if you call it with

GetData2(1, 2, 3)

or with

GetData2(arg1=1, arg2=2, arg3=3)

or any other combination.

The call path is:

    wrapped GetData2()
--> Memoized.__call__()
--> self.func()
--> original GetData2()

Answer 2

At the very least there's a problem in how you pass parameters to __call__() . Try changing the *args in your __call()__ -function to **args . This means that instead of passing an arbitary tuple of arguments you'll pass keyword arguments as a dictionary.

class Memoized(object):
    def __init__(self, func):
        self.func = func
        self.cache = {}

    def __call__(self, **args):
        print args
        ....

This will then result in something like this:

In [16]: GetData2(**r)
{'arg1': 'hello', 'arg2': 67, 'arg3': 8.3}

However this might change the way you expect your caching routine to work.