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Date: Tue, 3 Jun 2014 01:55:52 +1000
Subject: Re: Obfuscated Python hack
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Tue, Jun 3, 2014 at 1:38 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Mon, 02 Jun 2014 23:23:53 +1000, Chris Angelico wrote:
>
>> On Mon, Jun 2, 2014 at 10:27 PM, Tim Chase
>> <python.list@tim.thechases.com> wrote:
>>> Stripping off the exec() call makes it pretty transparent that you're
>>> attempting (successfully on some platforms) to set the value of "4" to
>>> "5".  But a cute hack.
>>
>> And not on Windows inside IDLE, where attempting to use 4 results in a
>> ===== RESTART ===== crash.
>
> Sounds like a bug in IDLE.
>
> What happens if you try it in Windows without IDLE, just using the
> standard interactive interpreter?

It works fine without IDLE.

Python 2.7.4 (default, Apr  6 2013, 19:54:46) [MSC v.1500 32 bit (Intel)] on win
32
>>> exec((lambda *fs: reduce(lambda f, g: lambda x: f(g(x)), fs))(*([lambda s: s
[1::2]+s[-2::-2]]*54))('motcye;cye._n8fo_drs(d4+)vle=5  ua.8)(isedamr.ticspt spt
 rpi'))
>>> 10 - 6 == 10 - 5
True


In IDLE:

>>> exec((lambda *fs: reduce(lambda f, g: lambda x: f(g(x)), fs))(*([lambda s: s[1::2]+s[-2::-2]]*54))('motcye;cye._n8fo_drs(d4+)vle=5  ua.8)(isedamr.ticspt spt rpi'))
>>> 10 - 6 == 10 - 5

>>> ================================ RESTART ================================

There's a bit of a pause before the RESTART line comes through, and
repeating the equality check after that comes back with a
straight-forward False.

Running IDLE from a terminal gives this:

C:\Documents and Settings\M>\python27\python -m idlelib.idle

----------------------------------------
Unhandled server exception!
Thread: SockThread
Client Address:  ('127.0.0.1', 4414)
Request:  <socket._socketobject object at 0x0127ADC0>
Traceback (most recent call last):
  File "C:\python27\lib\SocketServer.py", line 295, in _handle_request_noblock
    self.process_request(request, client_address)
  File "C:\python27\lib\SocketServer.py", line 321, in process_request
    self.finish_request(request, client_address)
  File "C:\python27\lib\SocketServer.py", line 334, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "C:\python27\lib\idlelib\rpc.py", line 503, in __init__
    SocketServer.BaseRequestHandler.__init__(self, sock, addr, svr)
  File "C:\python27\lib\SocketServer.py", line 649, in __init__
    self.handle()
  File "C:\python27\lib\idlelib\run.py", line 268, in handle
    rpc.RPCHandler.getresponse(self, myseq=None, wait=0.05)
  File "C:\python27\lib\idlelib\rpc.py", line 280, in getresponse
    response = self._getresponse(myseq, wait)
  File "C:\python27\lib\idlelib\rpc.py", line 300, in _getresponse
    response = self.pollresponse(myseq, wait)
  File "C:\python27\lib\idlelib\rpc.py", line 424, in pollresponse
    message = self.pollmessage(wait)
  File "C:\python27\lib\idlelib\rpc.py", line 376, in pollmessage
    packet = self.pollpacket(wait)
  File "C:\python27\lib\idlelib\rpc.py", line 357, in pollpacket
    self._stage0()
  File "C:\python27\lib\idlelib\rpc.py", line 364, in _stage0
    self.bufneed = struct.unpack("<i", s)[0]
error: unpack requires a string argument of length 4

*** Unrecoverable, server exiting!
----------------------------------------


So... I'd say this isn't so much a bug in IDLE as a limitation:
"depends on the universe being sane". I mean, honestly. You just
changed the meaning of four! :)

ChrisA