Expanding instructions for list CLI override

[rohitgirdhar]

Motivation

I just spent a bunch of time debugging a command line override that involved nested lists (something like param='[["a", 1, 2], ["b", 2, 3]]', which gave me a hydra.errors.OverrideParseException: no viable alternative at input error until I removed the space between the 2 sublists. So this tip might help future users.

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Not needed

[omry]

Thanks for reporting @rohitgirdhar.
Please file issues for discussion before sending pull request.
In this case this is actually a bug, not a documentation issue.

[omry]

#836

[omry]

This is not a list, it's a quoted string that looks like one.

param='[["a", 1, 2], ["b", 2, 3]]'

This is a bit confusing because both Hydra and the shell and using quotes.

This is the correct form:

'param=[[a, 1, 2], [b, 2, 3]]'

The quotes here are for the shell, to make sure it sends this as a single command line argument.
Note that you don't need to quote a and b, This is not JSON.
I have a fix coming for this issue as a part of a bigger change to the grammar (#752).

[omry]

This is actually a list, but the way you present it confused even me :).

You can tell what the shell will send to Hydra using echo:

$ echo param='[["a", 1, 2], ["b", 2, 3]]'
param=[["a", 1, 2], ["b", 2, 3]]