[Tutor] __new__ and __init__

[Alan Gauld]

On 01/08/12 15:28, rail shafigulin wrote:

> I'm trying to understand how to use the two methods. I know that __new__
> is used to create an object, while __init__ to initialize. But I'm not
> sure what happens when I create an object.

Use print statements to find out...

 >>> class C(object):
...    def __new__(cls):
...        print 'in new'
...        return object.__new__(cls)
...    def __init__(slf): print 'in init'
...
 >>> c = C()
in new
in init
 >>>


> 1) Does it mean that __new__ and __init__ must have the same parameters?
> In this particular case __new__ and __init__ both have model_name and if
> I understand correctly when __new__ is called the rest of the parameters
> (air, tilt, cruise_control, etc) are absorbed by the *args argument.

That's right and I've never tried doing it differently
  - but again the >>> prompt and print are your friends

> 2) What happens if I don't use the same parameters, say in the case of
> __init__ I will remove model_name, will I still be able to call dx =
> CarModel("Fix DX")
>

The best way to be sure is to try it. That's the joy of an interactive 
prompt... you never need to guess.


-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/