Support PING in pubsub mode

[thomasst]

Fixes #249

[popravich]

Try removing ping from _PUBSUB_COMMANDS, that is the reason why pool tests are failing

[thomasst]

This will fail then though:

        is_pubsub = command in _PUBSUB_COMMANDS
        if self._in_pubsub and not is_pubsub:
>           raise RedisError("Connection in SUBSCRIBE mode")
E           aioredis.errors.RedisError: Connection in SUBSCRIBE mode

aioredis/connection.py:274: RedisError

Any other suggestions?

[popravich]

Yes, it will fail.
You can extend condition of that if to something like:

if self._in_pubsub and not (is_pubsub or is_ping):
    ...

[codecov]

Codecov Report

Merging #264 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #264      +/-   ##
=========================================
+ Coverage   96.88%   96.9%   +0.01%     
=========================================
  Files          57      57              
  Lines        7450    7463      +13     
  Branches      587     589       +2     
=========================================
+ Hits         7218    7232      +14     
+ Misses        172     171       -1     
  Partials       60      60

Impacted Files	Coverage Δ
tests/pubsub_commands_test.py	100% <100%> (ø)	⬆️
examples/py34/connection.py	93.01% <0%> (-0.17%)	⬇️
tests/sentinel_failover_test.py	88.72% <0%> (+0.75%)	⬆️
aioredis/locks.py	100% <0%> (+4.34%)	⬆️

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[thomasst]

Just pushed some fixes. I also wanted to get your opinion on the return value of ping(). Normally it returns the string "PONG" (which Redis returns). However, in pubsub mode is returns a (lower case) "pong" message, so for consistency reasons I chose to return the "PONG" string. We might also want to consider returning nothing or True (the regular Python Redis library returns True). What do you think?

[thomasst]

@popravich could you please take another look at this PR? Thanks!

[popravich]

Thanks,
Sorry for long delay