__init__ explanation please

Reedick, Andrew jr9445 at ATT.COM
Tue Jan 15 23:34:16 CET 2008


> -----Original Message-----
> From: python-list-bounces+jr9445=att.com at python.org [mailto:python-
> list-bounces+jr9445=att.com at python.org] On Behalf Of Lie
> Sent: Tuesday, January 15, 2008 5:03 PM
> To: python-list at python.org
> Subject: Re: __init__ explanation please
> 
> I've been in this Python mailing list for a few days, and I've noticed
> several things here: There are too many fundamentalist!
> 
> Don't play stupid and all, don't be a fundamentalist. It might be true
> that __init__ isn't a constructor and __new__ might be the constructor
> (some people even claimed __new__ is also not a constructor).
 

Purist is a better term.  Fundamentalist is three syllables closer to
Holy War.


> >From the base definition of a constructor: constructor is the creator
> of an object. In this case, __new__ is technically the constructor
> while __init__ is an initializer.
> 
> However, it is also to be noted that __init__ is what makes an object
> meaningful, and that makes it a constructor in a sense (while still
> technically a constructor). Without initialization, an object is
> meaningless, even if the definition of the initializer is to leave it
> as it is.


You don't need to have an __init__ defined.  A subclass has to
explicitly call the parent's __init__ or the parent's __init__ is never
run.  If the __init__ makes the object meaningful, then how meaningful
is an object without an __init__?  I'm pretty sure that an object
without an __init__ is still a viable, working object.


> If you can't be convinced with this argument, then I'd give you
> another that's a bit more Pythonic:
> DUCK TYPING: If it looks like a duck, walks like a duck, and quacks
> like a duck, it is a duck!


But you don't need __init__ to be a duck!


> >From the class programmer's point of view, __init__ acts like an
> object constructor in other languages, there is no significant
> difference between __init__ and constructor in other languages. 


How many times can you call an object's constructor in other languages?
__init__ can be called repeatedly.


__init__ is the last straw that breaks the camel's back.  Or rather, the
last method we see in the object creation process, and thus must be
'guilty' of being a constructor.  Only a fundamentalist would blame the
victim instead of the real criminal, __new__.


We're splitting hairs.  And I'm pretty sure that, aside from being a
spiffy thought experiment, no one cares as long as it works and makes
sense.   =)


Repeated for clarity:  smiley -->  =)  <-- smiley



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