LPOS: add new command

[aparcar]

fix #1353

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Does travis tests pass with this change (enable it first in your forked repo and wait for the travis build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Redis 6.0.6 will support a new command called LPOS

The command returns the index of matching elements inside a Redis list. By default, when no options are given, it will scan the list from head to tail, looking for the first match of "element". If the element is found, its index (the zero-based position in the list) is returned. Otherwise, if no match is found, NULL is returned.

This PR adds the command and tests

[aparcar]

Does $ tox pass with this change (including linting)?

  py27-plain: commands succeeded
  py27-hiredis: commands succeeded
ERROR:  py35-plain: InterpreterNotFound: python3.5
ERROR:  py35-hiredis: InterpreterNotFound: python3.5
ERROR:  py36-plain: InterpreterNotFound: python3.6
ERROR:  py36-hiredis: InterpreterNotFound: python3.6
  py37-plain: commands succeeded
  py37-hiredis: commands succeeded
ERROR:  py38-plain: InterpreterNotFound: python3.8
ERROR:  py38-hiredis: InterpreterNotFound: python3.8
  py-plain: commands succeeded
  py-hiredis: commands succeeded
  py3-plain: commands succeeded
  py3-hiredis: commands succeeded
ERROR:  flake8: InterpreterNotFound: python3.6

It somewhat passes I guess.

[aparcar]

Is the new or changed code fully tested?

I transferred the "official" redis tests, however no garbage inputs are tested. Is that required?

[aparcar]

Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

I copied the "official" documentation and it's rendered with sphinx. Are any release news file updates required?

[aparcar]

Does travis tests pass with this change (enable it first in your forked repo and wait for the travis build to finish)?

As Redis 6.0.6 isn't installed on the travis instance everything fails. Using Redis unstable branch should work for all Python versions.

[codecov-commenter]

Codecov Report

Merging #1354 into master will decrease coverage by 7.28%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master    #1354      +/-   ##
==========================================
- Coverage   92.76%   85.48%   -7.29%     
==========================================
  Files          20        7      -13     
  Lines        6581     3017    -3564     
==========================================
- Hits         6105     2579    -3526     
+ Misses        476      438      -38     

Impacted Files	Coverage Δ
redis/client.py	85.99% <73.68%> (-0.09%)	⬇️
redis/connection.py	81.40% <100.00%> (-0.35%)	⬇️
redis/exceptions.py	100.00% <100.00%> (ø)
redis/_compat.py	86.99% <0.00%> (-0.11%)	⬇️
redis/lock.py	100.00% <0.00%> (ø)
tests/test_lock.py
tests/test_encoding.py
tests/test_connection.py
tests/test_monitor.py
... and 5 more

---

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[RoeyPrat]

Let's wait until redis 6.0.6 is out, and the UT check that version, to review this.

[aparcar]

Redis 6.0.6 is now available.

[andymccurdy]

Just waiting on the official docker image for 6.0.6 to be released.

[aparcar]

Related docker-library/official-images#8400

[aparcar]

Seems to work fine now. I didn't touch any of the files which are mentioned in the codecov report...

[abrookins]

To get coverage reported correctly, you'll need to bump the redis version used in this Dockerfile: https://github.com/andymccurdy/redis-py/blob/master/docker/base/Dockerfile

[andymccurdy]

I don't know why codecov is complaining. I'm wondering if they don't have a great base after we changed how the coverage report is run in the docker PR. I'm going to merge this anyway as it's clear that this PR did not contribute to the lowering of the coverage percentage.

[aparcar]

Thank you!