[Python-ideas] Making it easy to prepare for PEP479

[Steven D'Aprano]

On Tue, May 19, 2015 at 11:06:03AM +1200, Greg Ewing wrote:
> Steven D'Aprano wrote:
> >After all, I might want to write:
> >
> >if sys.version != '3.7' and read_config('config.ini')['allow_jabberwocky']:
> >    from __future__ import jabberwocky
> 
> You might want to, but I would have no qualms about
> firmly telling you that you can't. Putting try:
> in front of a future import still doesn't introduce
> any executable code before it, whereas the above does.

"Set up a try...except block" is not executable? Then how does it, um, 
you know, set up the try...except block? :-)

"try" compiles to executable code. If you don't believe me:

def a():
    spam

def b():
    try:  spam
    except:  pass

from dis import dis
dis(a)
dis(b)

and take note of the SETUP_EXCEPT byte-code.

In any case, I think that neither of us wants to change the rules about 
what can precede a __future__ import, so hopefully the point is moot.


-- 
Steve