ast wrote:
> Hello
>
> In the following code found here:
> https://www.pythonsheets.com/notes/python-object.html
>
> __init__ is not invoked when we create an object
> with "o = ClassB("Hello")". I don't understand why.
> I know the correct way to define __new__ is to write
> "return object.__new__(cls, arg)" and not "return object"
>
>
> >>> class ClassB(object):
> ... def __new__(cls, arg):
> ... print('__new__ ' + arg)
> ... return object
> ... def __init__(self, arg):
> ... print('__init__ ' + arg)
> ...
>
> >>> o = ClassB("Hello")
> __new__ Hello
>
>
> Normaly, when running "o = ClassB("Hello")", we first run
> __call__ from type of ClassB which is type. This __call__
> method is supposed to launch __new__ from ClassB and then
> __init__ from classB too. The output of __new__ is mapped
> to self parameter of __init__.
> But it seems things don't work like that here. Why ?
__init__ is called only if __new__ returns an instance of ClassB:
"""
/* If the returned object is not an instance of type,
it won't be initialized. */
if (!PyType_IsSubtype(Py_TYPE(obj), type))
return obj;
type = Py_TYPE(obj);
if (type->tp_init != NULL) {
int res = type->tp_init(obj, args, kwds);
"""
https://github.com/python/cpython/blob/master/Objects/typeobject.c#L982
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