[Python-Dev] PEP 492 quibble and request

Steven D'Aprano steve at pearwood.info
Fri May 1 13:41:13 CEST 2015

On Wed, Apr 29, 2015 at 06:12:37PM -0700, Guido van Rossum wrote:
> On Wed, Apr 29, 2015 at 5:59 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> > On 30 April 2015 at 10:21, Ethan Furman <ethan at stoneleaf.us> wrote:
> > > From the PEP:
> > >
> > >> Why not a __future__ import
> > >>
> > >> __future__ imports are inconvenient and easy to forget to add.
> > >
> > > That is a horrible rationale for not using an import.  By that logic we
> > > should have everything in built-ins.  ;)
> >
> This response is silly. The point is not against import but against
> __future__. A __future__ import definitely is inconvenient -- few people I
> know could even recite the correct constraints on their placement.

Are you talking about actual Python programmers, or people who dabble 
with the odd Python script now and again? I'm kinda shocked if it's the 

It's not a complex rule: the __future__ import must be the first line of 
actual executable code in the file, so it can come after any encoding 
cookie, module docstring, comments and blank lines, but before any other 
code. The only part I didn't remember was that you can have multiple 
__future__ imports, I thought they all had to be on one line. (Nice to 
learn something new!)

> > 'as' went through the "not really a keyword" path, and
> > it's a recipe for complexity in the code generation toolchain and
> > general quirkiness as things behave in unexpected ways.
> >
> I don't recall that -- but it was a really long time ago so I may
> misremember (did we even have __future__ at the time?).

I have a memory of much rejoicing when "as" was made a keyword, and an 
emphatic "we're never going to do that again!" about semi-keywords. I've 
tried searching for the relevant post(s), but cannot find anything. 
Maybe I imagined it?

But I do have Python 2.4 available, when we could write lovely code like 

py> import math as as
py> as
<module 'math' from '/usr/lib/python2.4/lib-dynload/mathmodule.so'>

I'm definitely not looking forward to anything like that again.


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