inner classes in python as inner classes in Java

[Daniel Dittmar]

> Carlo v. Dango wrote:
>> I want the semantics of java's inner classes and the semantics of
>> inner methods... that the inner class shares the fields and methods
>> of its outer class instance.. But I've come to realize I can't do
>> this in python, as

Alex Martelli wrote:
> I don't understand what you mean.  "inner methods" (? presumably you
> mean nested functions ?) cannot re-bind names in outer scope -- you
> say you want these semantics, and you also seem to say you DO want
> assignments on the innerobject's attribute to re-bind attributes on
> the outer.  There is a contradiction here in what you say.  Neither
> in Python nor with any other tools whatsoever can you implement
> contradictory requirements.

Inner classes (not static inner classes) in Java work as follows:
- the inner class has a reference to an object of the enclosing class
- any identifier is searched in the method scope, the inner class scope, the
enclosing class scope, so an identifier A can mean A (local), this.A
(inner), this.__enclosing__.A (enclosing), depending on where the compiler
finds it.

A Python implementation for inner classes would be:
class Inner:
    def __init__ (self, enclosing):
        self.__enclosing__ = enclosing

    def __getattr__ (self, name):
        return getattr (self.__enclosing__, name)

    def __setattr__ (self, name, value):
        if hasattr (self.__enclosing__):
            setattr (self.__enclosing__, name, value)
        else:
            setattr (self, name, value)

Java hides the 'enclosing' when creating objects, so
new Inner ()
becomes
new Inner (this)

Not that I think that hiding the real access path is a good idea.

Daniel