First of all, this is not a duplication of Why is __init__ not called after __new__ SOMETIMES because this question really is about the implementation of the build-in object class.
Here is the full story:
I am learning about __new__ vs __init__ in python. Here is the example I've tried:
class A(object):
def __new__(cls):
print("A.__new__ called")
return super(A, cls).__new__(cls)
def __init__(self):
print("A.__init__ called")
A()
print('finished')
The output is
A.__new__ called
A.__init__ called
finished
I understand that __new__ does object creation and __init__ does object initialization.
__new__ is called automatically when calling the class name. Then __init__ is called every time an instance of the class is returned by __new__, passing the returned instance to __init__ as the self parameter.
Knowing this, if we have a bad __new__ function that does not create and return an object instance, then __init__ would not be called:
class A(object):
def __new__(cls):
print("A.__new__ called")
#return super(A, cls).__new__(cls)
def __init__(self):
print("A.__init__ called")
A()
Note that the __new__ method only prints a string. It does not return anything so __init__ has nothing to pick up. And indeed the output confirms this:
A.__new__ called
finished
"A.__init__ called" is never printed so __init__ is indeed never called.
Now if we do not define a __new__ method (this is 99% of the common use case. programmers rarely need to define this method), then the father's __new__ is called by default. e.g.
class A(object):
def __init__(self):
print("A.__init__ called")
A()
print('finished')
output is:
A.__init__ called
finished
In this case the __new__ of built-in object class is called.
BUT, as I looked at the how the built-in object class is defined, I see this:
class object:
""" The most base type """
def __delattr__(self, *args, **kwargs): # real signature unknown
""" Implement delattr(self, name). """
pass
...
...
...
@staticmethod # known case of __new__
def __new__(cls, *more): # known special case of object.__new__
""" Create and return a new object. See help(type) for accurate signature. """
pass
NOTHING is implemented in the __new__! There is just a pass sitting inside !!??
How is this making sense?
