python中的类装饰器装饰方法

这个问题已经在这里有了答案：            >            How can I decorate an instance method with a decorator class?                                    3个
我正在尝试使用装饰器进行记忆,该装饰器是一个类而不是一个函数,但出现错误

TypeError: seqLength() takes exactly 2 arguments (1 given)

我猜想这与类有关,但是不确定那里出了什么问题.

编码：

import sys

class memoize(object):
    '''memoize decorator'''
    def __init__(self, func):
        self.func = func
        self.cache = {}
    def __call__(self, *args):
        try:
            return self.cache[args]
        except KeyError:
            value = self.func(self, *args)
            self.cache[args] = value
            return value

class collatz(object):
    def __init__(self, n):
        self.max = 1
        self.n = n
    @memoize
    def seqLength(self, n):
        if n>1:
            if n%2 == 0:
                return 1+self.seqLength(n/2)
            else:
                return 1+self.seqLength(3*n+1)
        else:
            return 1
    def maxLength(self):
        for n in xrange(1, self.n):
            l = self.seqLength(n)
            if l > self.max:
                self.max = n
        return self.max

n = int(sys.argv[1])
c = collatz(n)
print c.maxLength()

解决方法:

装饰器只是foo = decorator(foo)的语法糖,因此在这种情况下,您最终要使seqLength的自身成为备忘录而不是collat​​z.您需要使用描述符.该代码对我有用：

class memoize(object):
    '''memoize descriptor'''
    def __init__(self, func):
        self.func = func

    def __get__(self, obj, type=None):
        return self.memoize_inst(obj, self.func)

    class memoize_inst(object):
        def __init__(self, inst, fget):
            self.inst = inst
            self.fget = fget

            self.cache = {}

        def __call__(self, *args):
            # if cache hit, done
            if args in self.cache:
                return self.cache[args]
            # otherwise populate cache and return
            self.cache[args] = self.fget(self.inst, *args)
            return self.cache[args]

有关描述符的更多信息：

http://docs.python.org/howto/descriptor.html#descriptor-example

标签：decorator,memoization,python
来源： https://codeday.me/bug/20191201/2084056.html