[issue34314] Like __hash__, allow setting MyClass.__init__ to None to prevent it being called by type.__call__

[Raymond Hettinger]

Raymond Hettinger <raymond.hettinger at gmail.com> added the comment:

> Right now, you really gotta jump through hoops
> in some cases if you only want to use __new__ 
> and don't care about __init__ 

I'm now sure I see the difficulty. It is easy to define a classes with __new__ and without __init__:

    >>> class A:
            def __new__(cls, *args):
                print('New called with', cls, 'and', args)
                return object.__new__(cls)

    >>> a = A(10, 20, 30)
    New called with <class '__main__.A'> and (10, 20, 30)
    >>> isinstance(a, A)
    True

> Like __hash__, allow setting MyClass.__init__ to None

FWIW, the API for hashing being set-to-None wasn't done because we like it (there a numerous downsides). It was done because we needed hashing to be on by default and there needed to be a way to turn it off.  The downsides are that it confuses users, it is hard to teach and remember, and it adds a branch to various APIs which would then need to test for None.  Instead, we prefer the pattern of having object() provide a default dummy method that either does nothing or gives up (like object.__init__ or the various rich comparison methods for object).  This simplifies downstream code than doesn't have to check for a rare special case.

----------
assignee:  -> rhettinger
nosy: +rhettinger

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34314>
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