Re: def init(self):

From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Subject	Re: def __init__(self):
Date	2016-04-27 03:04 +1000
Message-ID	<mailman.117.1461690250.32212.python-list@python.org> (permalink)
References	(6 earlier) <1461687967.2507874.590200129.102244C8@webmail.messagingengine.com> <mailman.114.1461687970.32212.python-list@python.org> <571f9836$0$1619$c3e8da3$5496439d@news.astraweb.com> <CALvWhxtRM+Qd983o2eB2SC4Hk0EsU26t-zbOQFW23a27Z3gx3Q@mail.gmail.com> <CAPTjJmoaJWHaXz_6jVoGzCm9Y4C+b5a=4C8gHoxt9B=jxQpJGQ@mail.gmail.com>

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On Wed, Apr 27, 2016 at 2:59 AM, Chris Kaynor <ckaynor@zindagigames.com> wrote:
> On Tue, Apr 26, 2016 at 9:32 AM, Steven D'Aprano <steve@pearwood.info>
> wrote:
>
>> Subclassing immutable built-ins is the most obvious and simple (and
>> probably
>> common) way to get an immutable class. Actually immutable, short of doing
>> wicked things with ctypes.
>>
>
> By wicked things with ctypes, do you mean something like this? By no means
> do I suggest this actually be used by anybody for any reason.
>
> Tested with '2.7.10 (default, Jul 14 2015, 19:46:27) \n[GCC 4.2.1
> Compatible Apple LLVM 6.0 (clang-600.0.39)]'
>
> import ctypes
> def changeTuple(tuple, index, newValue):
>     obj = ctypes.cast(id(tuple), ctypes.POINTER(ctypes.c_long))
>     obj[3+index] = id(newValue)
>
>>>> a = ('a','b','c')
>>>> changeTuple(a, 0, 1)
>>>> a
> (1, 'b', 'c')
>>>> changeTuple(a, 1, 3)
>>>> a
> (1, 3, 'c')

Yeah. By the look of things, you've just destroyed the reference counts.

>>> a = ('a','b','c')
>>> b = object()
>>> changeTuple(a, 0, b)
>>> a
(<object object at 0x7f1240b22080>, 'b', 'c')
>>> del b
>>> a
Segmentation fault

ChrisA

Thread

def __init__(self): San <santanu01@gmail.com> - 2016-04-25 23:21 -0700
  Re: def __init__(self): Ben Finney <ben+python@benfinney.id.au> - 2016-04-26 16:31 +1000
  Re: def __init__(self): Gary Herron <gherron@digipen.edu> - 2016-04-26 00:06 -0700
  Re: def __init__(self): Ben Finney <ben+python@benfinney.id.au> - 2016-04-26 17:34 +1000
    Re: def __init__(self): Marko Rauhamaa <marko@pacujo.net> - 2016-04-26 11:25 +0300
      Re: def __init__(self): Steven D'Aprano <steve@pearwood.info> - 2016-04-27 02:12 +1000
        Re: def __init__(self): Random832 <random832@fastmail.com> - 2016-04-26 12:26 -0400
          Re: def __init__(self): Steven D'Aprano <steve@pearwood.info> - 2016-04-27 02:32 +1000
            Re: def __init__(self): Chris Kaynor <ckaynor@zindagigames.com> - 2016-04-26 09:59 -0700
              Re: def __init__(self): Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-04-27 14:54 +1000
            Re: def __init__(self): Chris Angelico <rosuav@gmail.com> - 2016-04-27 03:04 +1000
            Re: def __init__(self): Chris Kaynor <ckaynor@zindagigames.com> - 2016-04-26 10:13 -0700
            Re: def __init__(self): Ian Kelly <ian.g.kelly@gmail.com> - 2016-04-26 11:26 -0600
            Re: def __init__(self): Chris Angelico <rosuav@gmail.com> - 2016-04-27 03:30 +1000
        Re: def __init__(self): Marko Rauhamaa <marko@pacujo.net> - 2016-04-26 19:38 +0300
  Re: def __init__(self): Random832 <random832@fastmail.com> - 2016-04-26 09:49 -0400
  Re: def __init__(self): Gary Herron <gherron@digipen.edu> - 2016-04-26 07:25 -0700

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