Calling constructor but not initializer

[Steve Holden]

Steven D'Aprano wrote:
> I have a class that has a distinct "empty" state. In the empty state, it 
> shouldn't have any data attributes, but it should still have methods.
> 
> The analogy is with a list: an empty list still has methods like append() 
> etc. but it has no "data", if by data you mean items in the list.
> 
> I can construct an empty instance in the __new__ constructor, and I can 
> initialize an non-empty instance in the __init__ initializer, but I can't 
> think of any good way to stop __init__ from being called if the instance 
> is empty. In pseudo-code, I want to do something like this:
> 
> class Parrot(object):
>     def __new__(cls, data):
>         construct a new empty instance
>         if data is None:
>             return that empty instance
>         else:
>             call __init__ on the instance to populate it
>             return the non-empty instance
> 
> 
> but of course __init__ is automatically called.
> 
> 
> Any suggestions for doing something like this?
> 
> 
Easy: use a method whose name is something other than __init__, then 
don't bother to implement __init__. Note that __new__ shouldn't call 
__init__ anyway, that's done by the instance creation mechanism.

regards
  Steve
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Sorry, the dog ate my .sigline