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Date: Thu, 28 May 2015 19:06:09 +1000
Subject: Re: Returning a custom file object (Python 3)
From: Chris Angelico <rosuav@gmail.com>
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On Thu, May 28, 2015 at 5:04 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
>> This does appear to work. Whether or not it's a good idea is a
>> separate question.
>
>
> And this is EXACTLY the sort of use-case that having __class__ be writable
> is intended to solve. So this is exactly the solution I was after, thank
> you. Er... except for one little problem... in Python 3.3:
>
> py> f = open("/tmp/a", "r")
> py> f.__class__ = MyFile
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: __class__ assignment: only for heap types
>
>
> So it doesn't work for me. What version of Python are you using?

Huh, didn't even think to check other versions.

$ python3
Python 3.5.0b1+ (default:7255af1a1c50+, May 26 2015, 00:39:06)
[GCC 4.9.2] on linux

It's a build fresh from source control around about this weekend (some
time after feature freeze, obviously, but beyond that all I know is
what you see there). I guess this is pretty new; trying the same thing
on 3.4.2 doesn't work. But hey! 3.5 will be out soon...

ChrisA