[Python-ideas] sys.py3k

Steven D'Aprano steve at pearwood.info
Sun Nov 4 23:33:42 CET 2012

On 05/11/12 08:49, anatoly techtonik wrote:
> if sys.py3k:
>    # some py2k specific code
>    pass

Do you expect every single Python 3.x version will have exactly the same
feature set? That's not true now, and it won't be true in the future.

In my option, a better approach is more verbose and a little more work, but
safer and more reliable: check for the actual feature you care about, not
some version number. E.g. I do things like this:

# Bring back reload in Python 3.
except NameError:
     from imp import reload

Now your code is future-proofed: if Python 3.5 moves reload back into
the builtins, your code won't needlessly replace it. Or if you're running
under some environment that monkey-patches the builtins (I don't know,
IDLE or IPython or something?) you will use their patched reload instead
of the one in the imp module.

Or I go the other way:

except NameError:
     # Python 2.4 compatibility.
     def any(items):
         for item in items:
             if item:
                 return True
         return False

Now if I'm running under a version of 2.4 that has backported the
"any" function, I will prefer the backported version to my own.


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