__init__ is the initialiser
greg.ewing at canterbury.ac.nz
Tue Feb 4 00:47:12 CET 2014
Steven D'Aprano wrote:
> # --- Untested ---
> # Automatically call each __new__ constructor method, starting from
> # the most fundamental (object) and ending with the current class.
> stack = 
> for c in cls.__mro__:
> if hasattr(c, '__new__'):
> while stack:
That sort of thing doesn't allow for passing different
arguments to the base __new__.
Also remember that in Python, __new__ isn't actually
required to call a matching base version at all -- it's
legal to do something quite different, such as returning
a cached instance or instantiating a different type of
> What I meant by backwards compatibility is that prior to the introduction
> of new-style classes, you couldn't override __new__, only __init__. So if
> you had a classic class, you'd have to receive the instance:
> class Classic:
> def __init__(self, *args):
> but for new-style classes, you'd receive the class:
> class Newstyle(object):
> def __init__(cls, *args):
What I'm saying is that even if all classes had been
new-style from the beginning, it's by no means certain that
Guido wouldn't have come up with the __new__/__init__
system anyway, because of the flexibility it provides.
Python isn't the only language to do something like that.
In Objective-C, the basic pattern for instantiating an
object goes like
[[SomeClass alloc] init: args]
where 'alloc' allocates memory for the object and
'init:' or some variation thereof initialises it.
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