描述符的方法 [英] Methods on descriptors

问题描述

我正在尝试围绕 redis 数据库实现一个包装器，该数据库进行一些簿记，并且我考虑过使用描述符.我有一个包含一堆字段的对象:帧、失败等，我需要能够获取、设置，并根据需要增加字段.我试图实现一个 Int-Like 描述符:

I'm trying to implement a wrapper around a redis database that does some bookkeeping, and I thought about using descriptors. I have an object with a bunch of fields: frames, failures, etc., and I need to be able to get, set, and increment the field as needed. I've tried to implement an Int-Like descriptor:

class IntType(object):
    def __get__(self,instance,owner):
        # issue a GET database command
        return db.get(my_val)

    def __set__(self,instance,val):
        # issue a SET database command
        db.set(instance.name,val)

    def increment(self,instance,count):
        # issue an INCRBY database command
        db.hincrby(instance.name,count)

class Stream:
    _prefix = 'stream'
    frames = IntType()
    failures = IntType()
    uuid = StringType()

s = Stream()

s.frames.increment(1)  # float' object has no attribute 'increment'

似乎我无法访问我的描述符中的 increment() 方法.我不能在 __get__ 返回的对象中定义增量.如果我想做的只是增加，这将需要一个额外的数据库查询！我也不想在 Stream 类上使用 increment() ，因为稍后当我想在 Stream 中有额外的字段(如字符串或集合)时，我需要键入检查所有内容.

Is seems like I can't access the increment() method in my descriptor. I can't have increment be defined in the object that the __get__ returns. This would require an additional db query if all I want to do is increment! I also don't want increment() on the Stream class, as later on when I want to have additional fields like strings or sets in Stream, then I'd need to type check the heck out of everything.

推荐答案

试试这个:

class IntType(object):
    def __get__(self,instance,owner):
        class IntValue():

            def increment(self,count):
                # issue an INCRBY database command
                db.hincrby(self.name,count)

            def getValue(self):
                # issue a GET database command
                return db.get(my_val)

        return IntValue()

   def __set__(self,instance,val):
       # issue a SET database command
       db.set(instance.name,val)

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