Using Python 2

[Chris Angelico]

On Sat, Sep 9, 2017 at 2:19 AM, Steve D'Aprano
<steve+python at pearwood.info> wrote:
> On Sat, 9 Sep 2017 12:41 am, Chris Angelico wrote:
>
>>> I ran 2to3 on some code that worked under 2.6.6. and 3.6.2. 2to3 broke it
>>> for both versions and it was a fairly trivial script.
>>
>> Show the code that it broke? I've never seen this, unless it's
>> something like "now you need to install third-party package X in
>> Python 3". The 2to3 transformations are fine for everything in the
>> stdlib.
>
> Chris, I don't think it is controversial that 2to3 occasionally breaks code, or
> fails to translate every feature. Even today, there are still the occasional
> bug report or feature request for 2to3.

For "a fairly trivial script", I would like to see how it breaks it.
The only thing I've seen that frequently causes trouble is the
bytes/text distinction (which, if we're honest, is really just
exposing a problem that was already there), and that's only if you
have a boundary that can't be trivially resolved eg by adding
encoding="utf-8" to your file open calls.

> One thing which is notoriously tricky to migrate is mixed bytes/Latin1 text
> using Python 2 strings, say you're manipulating file formats that mix text with
> binary bytes. These mixed binary/text files are sometimes badly suited to the
> new Unicode/bytes model.

Yes - but I don't expect to see a true mixture of binary and textual
data in "a fairly trivial script". That sort of thing comes up when
you develop parsers for certain network protocols or file formats, but
I don't call those "trivial".

I should have been more clear about my comment there - that it was
specific to the complaint that 2to3 broke a trivial script.

ChrisA