no return values for __init__ ??

[Helge Hess]

"Fred L. Drake, Jr." wrote:
> Helge,
>   Yes:  It doesn't make sense. 

Well, IMHO it does make sense, see below.

> The job of the __init__() method is to
> initialize the instance which has already been created. 

Why should we have this distinction ? I find it inconsistent to declare
'__init__' to behave differently from other methods. *This* doesn't make
sense to me.

> There is no
> way for a Python program to receive the return value.

In the current interpreter not. That is what annoys me, since it is an
completly articial limitation I don't understand.
As mentioned it took only 5 minutes to 'correct' this limitation.

>   To implement the singleton pattern you appear to be interested in,
> try this:

[singleton using function]
>         def C():
>             global _C_singleton

This example covers only the most basic case and is a hack (eg how do I
do 'o instanceof C' ?). The idea behind returning a value different from
'self' or 'None' is to customize the class based on the parameters.

eg:
  class ImmutableDictionaryClass: # this is abstract
    def __init__(self, keys, values):
      if len(keys) == 0:
        # always return the same empty dict to save memory
        if emptyImmutableDict is None: 
          emptyImmutableDict = EmptyImmutableDict()
        return emptyImmutableDict
      elif len(keys) < 10:
        return SequentialDictionary(keys, values)
      else:
        return HashTableDictionary(keys, values)

This is called a 'class-cluster' in Objective-C and has quite some
advantages. Another useful application for clusters are string-objects
(different classes for different char widths, eg Py8bitString,
PyUnicodeString, ..)

The nice thing is that you only need a single (abstract) class to
interact with. Defining a function like you did above seems
unnecessarily hackish to me.

Notably removing the constraint in the interpreter doesn't affect
existing Python code ! This is what I wonder about. The interpreter was
apparently restricted intentionally in this regard and I wonder what
lead to this decision.

best regards
  Helge
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