variable six.PY3 -- is time bomb :)

[benjaminp]

Originally reported by: Andrej Antonov (Bitbucket: polymorphm, GitHub: polymorphm)

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good day!

variable six.PY3 -- is time bomb :)

file six.py now has code:

# True if we are running on Python 3.
PY3 = sys.version_info[0] == 3

...but must be somewhere like:

# True if we are running on Python version at least 3.
PY3 = sys.version_info[0] >= 3

thanks in advance! (and sorry for my bad english :))

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• Bitbucket: https://bitbucket.org/gutworth/six/issue/22

[benjaminp]

It would be inaccurate to have a true PY3 variable in hypothetical Python 4. six will be long dead and forgotten by the time Python 4 rolls around. (At that point I will have to write "twelve".)

[benjaminp]

Original comment by Andrej Antonov (Bitbucket: polymorphm, GitHub: polymorphm):

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ok :) .. I can only hope that in the "twelve" will be code line:

PY4 = sys.version_info[0] >= 4

or

PY4 = sys.version_info[0] != 3

[benjaminp]

Original comment by Collin Anderson (Bitbucket: collinmanderson, GitHub: Unknown):

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"six will be long dead and forgotten by the time Python 4 rolls around." -- I hope :). There may be people who hold out until 2020 before starting to use six, and Python 4 is scheduled for 2023.

[benjaminp]

Why do you think Python 4 is scheduled?

[benjaminp]

Original comment by Collin Anderson (Bitbucket: collinmanderson, GitHub: Unknown):

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Sorry. "Scheduled" is the wrong work. I'm just referring to Nick's estimate http://developerblog.redhat.com/2014/09/17/why-python-4-0-wont-be-like-python-3-0/

Anyway, I suppose there's no rush in dealing with the issue now.

[benjaminp]

Original comment by astrofrog (Bitbucket: astrofrog, GitHub: astrofrog):

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Just for info, I wrote a blog post today on the use of six.PY3 and sys.version_info[0] == 3:

http://astrofrog.github.io/blog/2016/01/12/stop-writing-python-4-incompatible-code/

In my opinion, PY3 is fine as it is and it would be weird for PY3 to be True on Python 4. The better solution is just to write code like:

if six.PY2:
    # Python 2 code
else:
    # Python 3 code

[stxlvt]

I want to add my partial support to @astrofrog and @polymorphm on this issue. I repeated the github search, and find close to one million matches for if six.PY3. And that's just one of several equivalent ways to write it. I would also like to link to this related issue for context.

I think it's unrealistic to expect enough of those people to fix their code in the roughly 3.5 years remaining until we may start seeing development releases of python 4.0, and I think both python 2.7 and six will still be alive and kicking when that time comes.

Look how everybody uses the PY3 constant as if it was called NOT_PY2. I feel confident in saying that none of those who write it intends it to mean if PY3 and not PY4. I agree with astrofrog that it would be weird for it to behave as @polymorphm suggests when it's called PY3, but even so I think in this case practicality beats purity and the actual usage should guide this decision. The code search clearly shows that it would break expectations for PY3 to be False on python 4. Therefore you really ought to change the definition to

PY3 = sys.version_info[0] >= 3

... and update the documentation to match.

[stxlvt]

I notice did not mention @benjaminp in the above comment, so he likely didn't see it and can't consider reopening this issue. Hence this comment.

[jaraco]

PY3 is still a time bomb and I'm starting to get pull requests to remove the use of PY3. I can't tell you how excited I am about the long tail of pull requests to replace PY3 with PY2. :(

[benjaminp]

What other people spend their time making PRs for is rather out of my hands.