Alan Kay on OOP

If I recall correctly, the notion of OOP by Alan Kay was discussed not
long ago in comp.lang.python.  Stefan Ram shared an amazing e-mail reply
given to him by Alan Kay himself.  The e-mail was very enlightening, but
I've spent quite some time on the last paragraph, which I'm still far
from understanding.

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Date: Wed, 23 Jul 2003 09:33:31 -0800
To: Stefan Ram [removed for privacy]
From: Alan Kay [removed for privacy]
Subject: Re: Clarification of "object-oriented"
[some header lines removed for privacy]
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[...]

    What does "object-oriented [programming]" mean to you?
    (No tutorial-like introduction is needed, just a short
    explanation [like "programming with inheritance,
    polymorphism and encapsulation"] in terms of other concepts
    for a reader familiar with them, if possible. Also, it is
    not neccessary to explain "object", because I already have
    sources with your explanation of "object" from
    "Early History of Smalltalk".)

(I'm not against types, but I don't know of any type systems that
aren't a complete pain, so I still like dynamic typing.)

OOP to me means only messaging, local retention and protection and
hiding of state-process, and extreme late-binding of all things. It
can be done in Smalltalk and in LISP. There are possibly other
systems in which this is possible, but I'm not aware of them.

Cheers,

Alan
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I've read the Early History of Smalltalk, by the way.  I think I
understand what he means by ``messaging'', ``local retention and
protection'' and ``hiding of state-process''.  My knowledge reaches its
limits a bit in ``extreme late-binding of all things'' and I get
certainly puzzled in ``it can be done in Smalltalk and in LISP'' given
that he is ``not aware of [others]''.

I think he mentions late-binding because I suppose that is required for
OOP in static languages like C++, say.  But I would like to get a clear
undertanding of what is early and late binding, so I probably should
look at a text book with examples---homework for me to and I would be
grateful if anyone wants to be my adviser here and point out a specific
book or example.

Now, to address my main puzzle.  The email is from 2003.  Alan Kay was
certainly aware of Python, Java and so on.  Why would his notion of OOP
be impossible in Python or Java?

My attempt at answering such question is this: Python, for example,
doesn't enforce the hiding of state-process because there's no true
private members in objects---on purpose.  Is that a reason why Python
fails to satisfy Alan Kay's OOP?  So, his notion is that an object
should really be completely opaque---the only way *possible* to interact
with it would be to send it a message and possibly expect a returning
message.

In some lecture Alan Kay has given (to a class in a university in the
US, whose name I can't remember), I remember he mentioned the Internet
being a true OO system.  That reinforced my idea above: a computer
system cannot, for example, share state with one another in a direct way
if their means of communication is a protocol such as IP.

But I'm still puzzled.  Although I'm sure LISP can do anything any other
language ever could, it is also a language so hackable that any of its
rules can also be violated by a LISP programmer, unless perhaps if we
think of the programmer as the user of a certain interface whose
implementation he cannot touch.

Anyway, my objective here is to understand and be able to write examples
in languages such as Common Lisp and Python to illustrate what he means
by OOP.  Thanks for any contribution anyone can offer here.  Thanks!