[Python-ideas] Required to call superclass __init__

Neil Toronto ntoronto at cs.byu.edu
Tue Nov 13 17:09:31 CET 2007

Jim Jewett wrote:
> On 11/13/07, Oleg Broytmann <phd at phd.pp.ru> wrote:
>> On Tue, Nov 13, 2007 at 12:23:40AM -0700, Neil Toronto wrote:
>>> I've got a working prototype metaclass and class instance
>>> (require_super) and decorator (super_required).
> Is this restricted to __init__ (and __new__?) or could it be used on any method?

It can be used on any method.

> Is there (and should there be?) a way around it, by catching the
> TypeError?  By creating a decoy object to call super on?

Definitely should be, and I made one because I plan on using this 
myself. :) Currently, you can set self.<method>_super = True (or 
self.__<method>__super = True) instead of doing the superclass method 
call. (Yes, it currently litters the class instance with flags, but 
that's an implementation detail.) If you're not going to call the 
superclass method, you need to state that explicitly.

class C(B):
      def __init__(self):
          self.__init__super = True

c = C()  # No problem

I've fiddled with the idea of having a redecoration with @super_required 
remove the requirement from the current method but place it back on 
future overrides. Maybe a @super_not_required could remove it completely.

>>    Chicken and egg problem, in my eyes. If the user is clever enough to use
>> the class and the decorator isn't she clever enough to call inherited
>> __init__?
> It may not be the same user.
> A library or framework writer would create the base class and use the
> decorator to (somewhat) ensure that subclasses meet the full interface
> requirements.
> A subclass writer should call the super.__init__ because it is in the
> API, but Neil's metaclass makes it easier to debug if they forget.

Exactly so.


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