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Re: Deep vs. shallow copy?

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On Fri, Mar 14, 2014 at 11:08 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Thu, Mar 13, 2014 at 5:55 PM, Chris Angelico <rosuav@gmail.com> wrote:
>> I'm going to troll for a moment and give you a function that has no
>> return value.
>>
>> def procedure():
>>     raise Exception
>
>>>> import dis
>>>> dis.dis(procedure)
>   2           0 LOAD_GLOBAL              0 (Exception)
>               3 RAISE_VARARGS            1
>               6 LOAD_CONST               0 (None)
>               9 RETURN_VALUE

That's a return value in the same way that exec() has a return value
[1]. If somehow the raise fails, it'll return None.

>>>> def get_procedure_return_value():
> ...     """Returns the return value of procedure()."""
> ...     return procedure.__code__.co_consts[0]
> ...
>>>> print(get_procedure_return_value())
> None
>
> Look, there it is!

Succeeds by coincidence. From what I can see, *every* CPython function
has const slot 0 dedicated to None. At least, I haven't been able to
do otherwise.

>>> def function(x):
    return x*2+1

>>> import dis
>>> dis.dis(function)
  2           0 LOAD_FAST                0 (x)
              3 LOAD_CONST               1 (2)
              6 BINARY_MULTIPLY
              7 LOAD_CONST               2 (1)
             10 BINARY_ADD
             11 RETURN_VALUE
>>> function.__code__.co_consts
(None, 2, 1)

Your return value retriever would say it returns None still, but it doesn't.

Trollbridge: you have to pay a troll to cross.

ChrisA

[1] I'm not talking about Python's 'exec' statement, but about the
Unix exec() API, eg execlpe() - see http://linux.die.net/man/3/exec

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Thread

Deep vs. shallow copy? Alex van der Spek <zdoor@xs4all.nl> - 2014-03-12 14:25 +0000
  Re: Deep vs. shallow copy? Skip Montanaro <skip@pobox.com> - 2014-03-12 09:48 -0500
  Re: Deep vs. shallow copy? Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-03-12 10:00 -0500
    Re: Deep vs. shallow copy? Alex van der Spek <zdoor@xs4all.nl> - 2014-03-12 15:29 +0000
      Re: Deep vs. shallow copy? Wayne Brehaut <wbrehaut@mcsnet.ca> - 2014-03-12 13:06 -0600
      Re: Deep vs. shallow copy? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-12 23:07 +0000
        Re: Deep vs. shallow copy? Rustom Mody <rustompmody@gmail.com> - 2014-03-12 20:09 -0700
          Re: Deep vs. shallow copy? Ian <hobson42@gmail.com> - 2014-03-13 11:38 +0000
            Re: Deep vs. shallow copy? Rustom Mody <rustompmody@gmail.com> - 2014-03-13 08:28 -0700
              Re: Deep vs. shallow copy? random832@fastmail.us - 2014-03-13 13:25 -0400
        Re: Deep vs. shallow copy? Roy Smith <roy@panix.com> - 2014-03-13 07:44 -0400
          Re: Deep vs. shallow copy? Marko Rauhamaa <marko@pacujo.net> - 2014-03-13 14:27 +0200
            Re: Deep vs. shallow copy? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-13 23:41 +0000
              Re: Deep vs. shallow copy? Chris Angelico <rosuav@gmail.com> - 2014-03-14 10:55 +1100
                Re: Deep vs. shallow copy? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-14 01:41 +0000
              Re: Deep vs. shallow copy? Ian Kelly <ian.g.kelly@gmail.com> - 2014-03-13 18:08 -0600
              Re: Deep vs. shallow copy? Chris Angelico <rosuav@gmail.com> - 2014-03-14 11:22 +1100
                Re: Deep vs. shallow copy? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-14 01:59 +0000
              Re: Deep vs. shallow copy? Rustom Mody <rustompmody@gmail.com> - 2014-03-13 19:57 -0700
                Re: Deep vs. shallow copy? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-14 04:43 +0000
              Re: Deep vs. shallow copy? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-14 06:17 +0000
          Re: Deep vs. shallow copy? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-13 23:31 +0000

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