Support optional comment header for printed configs

[carmocca]

Pitch

Allow passing a function that returns an str so the config generated with --print_config has a comment header with that string.

This would be useful to save which version was used to generate a config inside the config itself.

$ python script.py --print_config
# a comment
# which might span
# multiple lines
# and is configurable
foo: 1

[mauvilsa]

Can you please explain more. Is the comment header one for the whole printed yaml? Why a function and based on what the string that returns changes?

Note that comments coming from docstrings are already included by using --print_config=comments. If an additional feature related to comments is added it would only be enabled by giving this option.

[carmocca]

The idea is to be able to add some metadata to the config file for reproducibility. For Lightning, it could include the version when the config file was generated:

# Lightning version: v1.4.1
trainer:
  ...
model:
  ...

Is the comment header one for the whole printed yaml?

Yes

Why a function and based on what the string that returns changes?

Actually this is not a hard requirement so passing the string directly is okay

Note that comments coming from docstrings are already included by using --print_config=comments. If an additional feature related to comments is added it would only be enabled by giving this option.

This would be okay as long as

• A --print_config=header is implemented, which would only include the header this PR requests. comments could include header + comments
• A default print_config value can be programatically set for the ArgumentParser. This way --print_config can default to --print_config=header

Although you could also expect that if this metadata/header is passed to the parser, it should be included in the config by default

[mauvilsa]

This has been implemented in commit 00f42e0. Based on the described use case it didn't make sense to have a switch in --print_config so it is only a property of the parser.