PEP suggestion: Uniform way to indicate Python language version

[rocky]

On Monday, August 22, 2016 at 1:36:07 AM UTC-4, Steven D'Aprano wrote:
> On Monday 22 August 2016 14:33, Chris Angelico wrote:
> 
> > On Mon, Aug 22, 2016 at 1:37 PM, rocky <rocky at gnu.org> wrote:
> >> Sorry should have been:
> >>
> >>  assert sys.version_info >= (3,0)
> > 
> > The next question is: How common is code like this? I don't put
> > version checks in any of my modules. Adding magic comments would be of
> > value only if this sort of thing is common enough to need its own
> > syntax.
> 
> Most of my code is supposed to work on Python 2.4 through the latest 3.x 
> version. That means I have lots of version-specific code.
> 
> But most of it uses feature detection rather than version checks. So instead of 
> writing:
> 
> if sys.version < '3':
>     def next(iterator):
>         return iterator.next()
> 
> 
> I write this:
> 
> try:
>     next
> except NameError:
>     def next(iterator):
>         return iterator.next()
> 
> or possibly this:
> 
> 
> if not hasattr(builtins, 'next'):
>     def next(iterator):
>         return iterator.next()
> 
> 
> But some features depend on new syntax, and you can't check for the 
> availability of new syntax at runtime. (Well, you can, by clever use of exec(), 
> but its too much trouble than its worth.) So very, very occasionally I have to 
> do a version check:
> 
> 
> if sys.version < '3':
>     import mymodule2 as mymodule
> else:
>     import mymodule3 as mymodule
> 
> 
> But... I don't understand what this proposal actually is. We already have a 
> uniform way to indicate the Python language version: check sys.version, or 
> sys.version_info, or sys.hexversion, whichever is more appropriate for your 
> needs.

The fact that you mention 3 different ways says to me this isn't uniform.

> Because this is just an ordinary comparison, you can then do whatever 
> you like, no matter how outlandish or unusual:
> 
> 
> if sys.version < '3':
>     try:
>         import mymodule3
>     except SyntaxError:
>         print("Yay, a syntax error!")
>     else:
>         print("Now that's weird, that shouldn't happen...")
>         del mymodule3
>     import mymodule2 as mymodule
> elif config[RUN_OLD_VERSION]:
>     import mymodule2 as mymodule
> else:
>     import mymodule3 as mymodule
> 
> 
> Could somebody (the OP?) please explain what is the purpose of this proposal, 
> what it does, how it works, and when would people use it?

All of the ways you mention involve running the program. Suppose you have a tool that analyzes source code. It reads the code, but doesn't run it. For example possibly code climate. How it it figure out which dialect of Python is being used? 

> 
> 
> 
> -- 
> Steve