ZOOKEEPER-3771: Update zk-merge-pr script to Python3

[tisonkun]

@eolivelli generally I use 2to3 util and check the codepath that I can arrive, manually fix some lines.

But it seems we can verify this patch totally when merging this patch :)

[eolivelli]

I will be happy to try out this patch for my next use of the script
thank you for your quick response !

[eolivelli]

can we keep the original file and add a new zk-merge-pr.py3 ?

[tisonkun]

@eolivelli i'd prefer a py2 and use py3 as py default.

[eolivelli]

Ok

[anmolnar]

Great work @tisonkun !
@eolivelli Why do you want to keep the python2 script? Source control does it for you for free.

[tisonkun]

Hi @anmolnar ! Here is part of the original mail

AFAIK python2 is EOL so maybe we can just have only python3 on master
and leave the old version on git repo

I can see one of the reasons we still have a py2 script is that possibly some of our committers still use py2 so that they can easily use the py2 script which keeps previous workflow. Though, a community lazy agreement might help on dropping it.

[eolivelli]

I agree with @tisonkun

[nkalmar]

I voted for v3 only on the mail list, but I agree we could keep v2 for a time, but maybe add a warning when script starts that it is deprecated?

[nkalmar]

{code}
commit_title = input("Commit title [%s]: " % pr_title.encode("utf-8")).decode("utf-8")
{code}
Doesn't work, no need to decode str in v3 anyomre, it throws an error. Might be other occurrences, please check. Thanks!

edit: removing just the decode only here worked for me, I managed to commit with python3 after this.

[tisonkun]

@nkalmar Thanks for your review and test. That is the only encode/decode pair on str. I pushed a follow-up commit to address it.

[enixon]

This looks good to me - super happy for py3 support.

[nkalmar]

LGTM, thanks @tisonkun !

[nkalmar]

Merged to master and branch-3.6 (branch-3.5 does not have the script in the repo). Thanks @tisonkun !