CLN: remove PY2

[jreback]

master issue for removing all vestigaes of Python 2.

After merging: #24942 (removing the PY2 CI jobs) and #25554 (bump numpy to 1.13.3), we will be ready to remove PY2 code, tests, and doc references.

Let's do this in bite sized pieces. IOW don't do a PR with changes for everything.

cc @pandas-dev/pandas-core

[TomAugspurger]

Have we discussed whether we continue to support 3.5? Matplotlib master seems to be on 3.6.

[WillAyd]

I think it would be great to jump to 3.6 eventually for better typing support, f-strings, dict ordering, etc... but at the same time I think it makes sense to rip out the Py27 chunks first before going that route, as there will be plenty as is to clean up

[jreback]

step by step here. Let's remove PY2 first. Agree not against dropping 3.5 but should not do all at once.

[TomAugspurger]

CF seems to have deprecated 3.5 building? http://conda-forge.org/docs/user/introduction.html#pinned-announcements Anaconda has stopped building 3.5 packages.

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On Thu, Mar 14, 2019 at 10:30 AM William Ayd ***@***.***> wrote: I think it would be great to jump to 3.6 eventually for better typing support, f-strings, dict ordering, etc... but at the same time I think it makes sense to rip out the Py27 chunks first before going that route, as there will be plenty as is to clean up — You are receiving this because you are on a team that was mentioned. Reply to this email directly, view it on GitHub <#25725 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABQHIiP4yYwqpjHFLSANkOOFUXYO5vgXks5vWmsagaJpZM4b0Bb6> .

[TomAugspurger]

That's actually affecting @h-vetinari's other PR; pytest wasn't being bumped correctly on the 3.5 build (since Anaconda doesn't have new enough 3.5 packages for it).

[jreback]

ok merged the removal of the CI jobs for PY2: #24942

open season on PY2 removals. but let's do this in a measured way.

cc @pandas-dev/pandas-core

[h-vetinari]

Before it's open season, I'd suggest to at least merge #25752 first - currently the CI is much reduced from what it was due to the requested hard deletion of PY2-jobs in #24942 (instead of replacing them with new CI jobs).

Another possible candidate to wait for is #25554 (which depends on #25752 in some sense).

[jreback]

do we have anything left of this?

cc @pandas-dev/pandas-core

[gfyoung]

@topper-123 went berserk on this issue, so probably he's a good one to judge this 🙂

[topper-123]

1. pandas.core.base.StringMixin is still there, I've given up on removing that one. If someone could take a look?
2. There's some remaining functions in pandas.compat. Some of these are not really compat functions and should be moved to other locations. For others I haven't completely checked if they could be removed
3. There are still comments containing the regex python2|python 2|PY2|PY 2 (52 instances total). The related code should be looked through for simplifications. Likewise the similar regex for Python3.
4. The issue tracker currently has 24 py2/3 compat issues. Some of these can be closed now, while other can be seen as notes that some patterns are possible now that python2 support has been dropped.

Else I don't see much systematic, but in a code base of this size, there is bound to be fragments here and there that people will just have to remove upon encountering them.

Resolution of points 3 and 4 require some effort as most of the issues are quite specific. Going through and closing those could perhaps be the subject of an online sprint?

[topper-123]

BTW, I don't necessarily see the above as blockers for a 0.25 release, but more like "things that should be cleaned up in order to have a tidy and modern code base". And doing them while there is a focus on python2/3 compat will probably be better than doing it "later".

[jreback]

this is not blocking 0.25; just seeing if we can close it :)

[jorisvandenbossche]

Since it is not blocking, moving this from the 0.25 milestone

[jbrockmendel]

closable?

[jreback]

sure

i don’t think we have anything concrete left that we want to remove