Re: Tail recursion to while iteration in 2 easy steps

From	Terry Reedy <tjreedy@udel.edu>
Subject	Re: Tail recursion to while iteration in 2 easy steps
Date	2013-10-04 18:32 -0400
References	(1 earlier) <87had0axxy.fsf@dpt-info.u-strasbg.fr> <CAMjeLr9KPf=Z4pJoQtU8LXiT686dABg-fpNoWYb9reEPRSsYjA@mail.gmail.com> <524C80B6.3010204@unistra.fr> <mailman.651.1380747919.18130.python-list@python.org> <87li292wnt.fsf@dpt-info.u-strasbg.fr>
Newsgroups	comp.lang.python
Message-ID	<mailman.732.1380925974.18130.python-list@python.org> (permalink)

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On 10/4/2013 5:49 AM, Alain Ketterlin wrote:

> I think allowing rebinding of function names is extremely strange,

Steven already countered the 'is extremely strange' part by showing that 
such rebinding is common, generally useful, and only occasionally dodgy 
and a candidate for being blocked.

I want to consider here what it would mean to concretely implement the 
abstract notion 'disallow rebinding of function names' and show what 
would be behind calling the idea 'not feasible'.

1. A 'name' is not a 'function name' unless the name is bound, at 
runtime, to a 'function'.

2. A 'function' in Python is not just one class but any callable object 
-- with with a __call__ methods. That comprises an unbounded set.

3. Python does not mandate how namespaces are implemented. CPython uses 
both dicts and, for function local namespaces, internal C arrays. So 
'names' in code can become either string keys for dicts or integer 
indexes for arrays.

4. Rebinding can be explicit ('='), implicit ('import', 'class', 'def'), 
*or hidden* (globals('a') = 1; ob.__dict__('a') = 1). The 'hidden' 
methods are intentional as they are sometimes needed*.  In CPython, 
these forms remain different in the byte code, but it could be 
otherwise. The point is that is may or may not be possible for the 
interpreter to even recognize a 'rebinding' in order to apply any 
rebinding blocking rule.

* There is no trick (that I know of) for hidden rebinding of function 
locals and nonlocals (short of using ctypes), but I am not sure that 
this is a language guarantee. However, I an sure that the absence is 
intentional.

 > even though it's easier to implement.

No kidding.

-- 
Terry Jan Reedy

Thread

Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-01 17:30 -0400
  Re: Tail recursion to while iteration in 2 easy steps rusi <rustompmody@gmail.com> - 2013-10-01 22:16 -0700
    Re: Tail recursion to while iteration in 2 easy steps Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-02 10:23 +0200
      Re: Tail recursion to while iteration in 2 easy steps rusi <rustompmody@gmail.com> - 2013-10-02 06:29 -0700
    Re: Tail recursion to while iteration in 2 easy steps Ravi Sahni <ganeshsahni07@gmail.com> - 2013-10-03 22:57 +0530
      Re: Tail recursion to while iteration in 2 easy steps rusi <rustompmody@gmail.com> - 2013-10-04 03:52 -0700
  Re: Tail recursion to while iteration in 2 easy steps Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-02 10:17 +0200
    Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-02 11:59 -0700
    Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-02 14:05 -0700
      Re: Tail recursion to while iteration in 2 easy steps Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-04 11:49 +0200
        Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-04 10:51 +0000
        Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-04 18:32 -0400
          Re: Tail recursion to while iteration in 2 easy steps Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-07 19:15 +0200
            Re: Tail recursion to while iteration in 2 easy steps Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-10-07 19:57 +0200
              Re: Tail recursion to while iteration in 2 easy steps Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-08 10:56 +0200
                Re: Tail recursion to while iteration in 2 easy steps Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-10-08 12:49 +0300
            Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-07 16:42 -0400
            Re: Tail recursion to while iteration in 2 easy steps random832@fastmail.us - 2013-10-07 17:19 -0400
              Re: Tail recursion to while iteration in 2 easy steps Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2013-10-08 10:41 +0200
            Re: Tail recursion to while iteration in 2 easy steps MRAB <python@mrabarnett.plus.com> - 2013-10-07 22:39 +0100
            Re: Tail recursion to while iteration in 2 easy steps Piet van Oostrum <piet@vanoostrum.org> - 2013-10-07 18:03 -0400
            Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-07 15:47 -0700
              Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-07 23:50 +0000
                Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-07 17:24 -0700
                Formal-ity and the Church-Turing thesis rusi <rustompmody@gmail.com> - 2013-10-07 20:17 -0700
                Re: Formal-ity and the Church-Turing thesis Ravi Sahni <ganeshsahni07@gmail.com> - 2013-10-08 10:46 +0530
                Re: Formal-ity and the Church-Turing thesis rusi <rustompmody@gmail.com> - 2013-10-07 22:44 -0700
                Re: Formal-ity and the Church-Turing thesis Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-10-08 07:43 +0100
                Re: Formal-ity and the Church-Turing thesis Ravi Sahni <ganeshsahni07@gmail.com> - 2013-10-08 18:31 +0530
                Re: Formal-ity and the Church-Turing thesis rusi <rustompmody@gmail.com> - 2013-10-08 06:33 -0700
                Re: Formal-ity and the Church-Turing thesis Steven D'Aprano <steve@pearwood.info> - 2013-10-08 07:50 +0000
                Re: Formal-ity and the Church-Turing thesis Ravi Sahni <ganeshsahni07@gmail.com> - 2013-10-08 18:16 +0530
                Re: Formal-ity and the Church-Turing thesis Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-08 13:11 +0000
                Re: Formal-ity and the Church-Turing thesis Robert Day <robertkday@gmail.com> - 2013-10-08 14:25 +0100
                Re: Formal-ity and the Church-Turing thesis Chris Angelico <rosuav@gmail.com> - 2013-10-09 08:36 +1100
                Re: Formal-ity and the Church-Turing thesis Mark Janssen <dreamingforward@gmail.com> - 2013-10-07 22:19 -0700
                Re: Formal-ity and the Church-Turing thesis rusi <rustompmody@gmail.com> - 2013-10-07 23:01 -0700
                Re: Formal-ity and the Church-Turing thesis Mark Janssen <dreamingforward@gmail.com> - 2013-10-08 10:39 -0700
                Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-07 17:16 -0700
                Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-08 02:36 +0000
                Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-07 20:27 -0700
                Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve@pearwood.info> - 2013-10-08 09:22 +0000
                Re: Tail recursion to while iteration in 2 easy steps Charles Hixson <charleshixsn@earthlink.net> - 2013-10-09 15:45 -0700
                Re: Tail recursion to while iteration in 2 easy steps Piet van Oostrum <piet@vanoostrum.org> - 2013-10-07 22:46 -0400
                Re: Tail recursion to while iteration in 2 easy steps Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-10-08 10:25 +0300
                Re: Tail recursion to while iteration in 2 easy steps Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-10-08 11:18 +0200
              Re: Tail recursion to while iteration in 2 easy steps Piet van Oostrum <piet@vanoostrum.org> - 2013-10-07 22:45 -0400
                Re: Tail recursion to while iteration in 2 easy steps Mark Janssen <dreamingforward@gmail.com> - 2013-10-07 20:34 -0700
    Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-02 18:17 -0400
      Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-03 01:24 +0000
        Re: Tail recursion to while iteration in 2 easy steps Dave Angel <davea@davea.name> - 2013-10-03 01:39 +0000
        Re: Tail recursion to while iteration in 2 easy steps MRAB <python@mrabarnett.plus.com> - 2013-10-03 02:46 +0100
          Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-03 02:34 +0000
            Re: Tail recursion to while iteration in 2 easy steps Chris Angelico <rosuav@gmail.com> - 2013-10-03 14:14 +1000
            Re: Tail recursion to while iteration in 2 easy steps random832@fastmail.us - 2013-10-03 10:16 -0400
            Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-03 15:04 -0400
        Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-02 22:41 -0400
          Re: Tail recursion to while iteration in 2 easy steps Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-10-04 01:30 +0000
        Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-02 23:06 -0400
        Re: Tail recursion to while iteration in 2 easy steps random832@fastmail.us - 2013-10-03 10:14 -0400
        Literal syntax for frozenset, frozendict (was: Tail recursion to while iteration in 2 easy steps) Ben Finney <ben+python@benfinney.id.au> - 2013-10-04 10:18 +1000
        Re: Literal syntax for frozenset, frozendict Ethan Furman <ethan@stoneleaf.us> - 2013-10-03 18:31 -0700
    Re: Tail recursion to while iteration in 2 easy steps Duncan Booth <duncan.booth@invalid.invalid> - 2013-10-03 14:52 +0000
      Re: Tail recursion to while iteration in 2 easy steps Neil Cerutti <neilc@norwich.edu> - 2013-10-03 16:03 +0000
        Re: Tail recursion to while iteration in 2 easy steps Duncan Booth <duncan.booth@invalid.invalid> - 2013-10-04 10:16 +0000
          Re: Tail recursion to while iteration in 2 easy steps Ian Kelly <ian.g.kelly@gmail.com> - 2013-10-04 04:41 -0600
          Re: Tail recursion to while iteration in 2 easy steps Ian Kelly <ian.g.kelly@gmail.com> - 2013-10-04 04:46 -0600
            Re: Tail recursion to while iteration in 2 easy steps Duncan Booth <duncan.booth@invalid.invalid> - 2013-10-04 11:16 +0000
          Re: Tail recursion to while iteration in 2 easy steps Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-10-04 14:11 +0300
          Re: Tail recursion to while iteration in 2 easy steps Terry Reedy <tjreedy@udel.edu> - 2013-10-04 17:14 -0400
          Re: Tail recursion to while iteration in 2 easy steps Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-10-05 09:39 +0200
          Re: Tail recursion to while iteration in 2 easy steps random832@fastmail.us - 2013-10-07 17:27 -0400
            Re: Tail recursion to while iteration in 2 easy steps Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-10-08 10:11 +0300
          Re: Tail recursion to while iteration in 2 easy steps Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2013-10-08 11:43 +0200

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