[Python-il] Where should Python 2/Py3 compatibility shims be placed?

[Shlomi Fish]

Hi all!

I sometimes put (per a hint I found on a web search) code like that at the
beginning of my Python programs:

if sys.version_info > (3,):
long = int
xrange = range

(e.g:
https://github.com/shlomif/project-euler/blob/master/project-euler/581/euler_581_v3.py#L4
)

This is a py2/py3 compatibility shim.

My question is whether I should put it only at the main program's file or also
at each and every *.py module that I load? I'm not sure I understand the python
handling of symbols well enough to answer that.

Thanks and happy holidays!

Shlomi Fish
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[Shai Berger]

Hi Shlomi,

On Saturday 08 April 2017 21:22:27 Shlomi Fish wrote:
>
> if sys.version_info > (3,):
> long = int
> xrange = range
>

> This is a py2/py3 compatibility shim.
>
> My question is whether I should put it only at the main program's file or
> also at each and every *.py module that I load? I'm not sure I understand
> the python handling of symbols well enough to answer that.
>

Such assignments, if done as you wrote, only affect the file they are in.

However, there are two ways in which You're Doing It Wrong(TM):

1) Rather than writing your own compatibility shims, use six[1], the de-facto-
standard compatibility library.

2) The specific snippet you wrote indicates that your code is essentially
Python 2, and you add shims to make it work under Python 3. But Python 2 is
going away, and the future is Python 3; you should write your programs as
Python 3 code, with shims to make them run under Python 2. This is also the
approach that six promotes.

Of course, shims only go so far, and if you want py2/py3 programs you have no
choice but to avoid certain py3 features and write the code in a "python 2"
way. But if you intend your code to live on, then it will be Python 2 support
which you'll drop at some point; you want that change to be as close as
possible to "just drop the shims".

Hope this helps,
Shai.

[1] https://pythonhosted.org/six/

[Shlomi Fish]

Hi Shai,

Thanks for your insights. I'll take them into consideration.

Regards,

Shlomi Fish

> Hope this helps,
> Shai.
>
> [1] https://pythonhosted.org/six/
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> Pyth...@hamakor.org.il
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