Python new-style-class-related question

Question

I am a python learner and currently hacking up a class with variable number of fields as in the "Bunch of Named Stuff" example here.

class Bunch:
    def __init__(self, **kwds):
        self.__dict__.update(kwds)

I also want to write a __setattr__ in this class in order to check the input attribute name. But, the python documentation says,

If __setattr__() wants to assign to an instance attribute, it should not simply execute "self.name = value" -- this would cause a recursive call to itself. Instead, it should insert the value in the dictionary of instance attributes, e.g., "self.__dict__[name] = value". For new-style classes, rather than accessing the instance dictionary, it should call the base class method with the same name, for example, "object.__setattr__(self, name, value)".

In that case, should I also use object.__dict__ in the __init__ function to replace self.__dict__?

Answer 1

No. You should define your class as class Bunch(object), but continue to refer to self.__dict__.

You only need to use the object.__setattr__ method while you are defining the self.__setattr__ method to prevent infinite recursion. __dict__ is not a method, but is an attribute on the object itself, so object.__dict__ would not work.

Answer 2

You can use

class Bunch:
    def __init__(self, **kwds):
        self.__dict__.update(kwds)

    def __setattr__(self, name, value):
        #do your verification stuff
        self.__dict__[name] = value

or with new-style class :

class Bunch(object):
    def __init__(self, **kwds):
        self.__dict__.update(kwds)

    def __setattr__(self, name, value):
        #do your verification stuff
        super(Bunch, self).__setattr__(name, value)