__setattr__在这个python代码中做了什么？

Question

这是我的代码:

class fun:

    def __getattr__(self,key):
        return self[key]

    def __setattr__(self,key,value):
        self[key] = value+1
a = fun()
a['x']=1
print a['x']

而错误是:

AttributeError: fun instance has no attribute '__getitem__'

当我把它改为:

class fun:

    def __getattr__(self,key):
        return self.key

    def __setattr__(self,key,value):
        self.key = value+1
a = fun()
a.x=1
print a.x

错误是:

RuntimeError: maximum recursion depth exceeded

我能做什么,我想得到 2

Answer 1

问题是self.key = ...调用__setattr__,所以你最终会进行无限递归.要使用__setattr__,您必须以其他方式访问对象的字段.有两种常见的解决方案:

def __setattr__(self,key,value):
    # Access the object's fields through the special __dict__ field
    self.__dict__[key] = value+1

# or...

def __init__(self):
    # Assign a dict field to access fields set via __[gs]etattr__
    self.attrs = {}

def __setattr__(self,key,value):
    self.attrs[key] = value+1