[Python-Dev] Proper initialization of structs

Nick Coghlan ncoghlan at gmail.com
Thu Oct 30 23:36:25 CET 2008

Alexandre Vassalotti wrote:
> On Thu, Oct 30, 2008 at 1:00 PM, Fred Drake <fdrake at acm.org> wrote:
>> It's good to move work into __init__ where reasonable, so that it can be
>> avoided if a subclass wants it done in a completely different way, but new
>> can't work that way.
> And that is exactly the reason why, the _pickle module doesn't use
> __new__ for initialization.  Doing any kind of argument parsing in
> __new__ prevents subclasses from customizing the arguments for their
> __init__.

No it doesn't - it just means the subclasses have to override __new__ as
well and then give the parent class the arguments it needs.

I've used this convention (*must* call parent class __new__ or the
instance will be broken, may call parent class __init__ if it is
helpful) many times, and it is far more robust than relying on
subclasses to remember to call the parent class __init__ when setting up
the class.


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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