On 26/09/2019 13:20, 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 ?
One more command to the REPL helps make things clearer:
>>> o
<class 'object'>
I would venture that o.__init__() is called, but object's __init__
doesn't do anything. On top of that, the language definition states
that "The return value of __new__() should be the new object instance
(usually an instance of cls)". You have returned the class object, not
an instance of anything, so on the whole it's lucky that
object.__init__() does nothing!
--
Rhodri James *-* Kynesim Ltd
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