Support variadic positional args when parsing from CLI

[jploskey]

Currently, it appears there's no way to take an arbitrary number of positional arguments when parsing settings from the command line. This is a blocker for me, migrating over from typer.

The closest you can get it by doing the following:

# test.py

from pydantic_settings import BaseSettings, CliPositionalArg, SettingsConfigDict


class Main(BaseSettings):
    model_config = SettingsConfigDict(
        cli_parse_args=True,
        cli_enforce_required=True,
    )

    values: CliPositionalArg[list[str]]


parsed = Main()
print(parsed.values)

However, this requires you to run it like python test.py a,b,c or python test.py '["a", "b", "c"]' rather than simply python test.py a b c, which usually makes more sense if the command only takes in a single list of values.

It would be nice to have something like a CliPositionalArgs type to support this:

# test.py

from pydantic_settings import BaseSettings, CliPositionalArgs, SettingsConfigDict


class Main(BaseSettings):
    model_config = SettingsConfigDict(
        cli_parse_args=True,
        cli_enforce_required=True,
    )

    values: CliPositionalArgs[list[str]]


parsed = Main()
print(parsed.values)

[hramezani]

@kschwab can you take look?

[kschwab]

@jploskey, thanks for the suggestion. I think the above is pretty straightforward to add. However, since internally we're based on argparse, it will likely run into issues for something like the below:

# test.py

from pydantic_settings import BaseSettings, CliPositionalArgs, SettingsConfigDict


class Main(BaseSettings):
    model_config = SettingsConfigDict(
        cli_parse_args=True,
        cli_enforce_required=True,
    )

    strings: CliPositionalArgs[list[str]]

    numbers: CliPositionalArg[list[int]]

#> test.py a b c 1 2 3

i.e., we could only support one variadic positional arg. Additionally, with a variadic positional, I think it also makes sense to reorder it to be the last positional, otherwise it will gobble up anything afterwards. e.g., if something like the below was provided, it would work with reordering:

# test.py

from pydantic_settings import BaseSettings, CliPositionalArgs, SettingsConfigDict


class Main(BaseSettings):
    model_config = SettingsConfigDict(
        cli_parse_args=True,
        cli_enforce_required=True,
    )

    strings: CliPositionalArgs[list[str]]

    number: CliPositionalArg[int]

#> test.py 1 a b c

If the above seems reasonable, we can head in that direction.

[jploskey]

@kschwab That makes sense and looks reasonable to me.

I think most common use cases for this (including mine) would be supported within those constraints. It'd be pretty rare to need two different variadic argument lists in the same command. And the only time I can think of wanting a non-variadic argument at the end of a command would be something like a "move" command like mv file-0 file-1 dir. But both of these cases could be (mostly) solved by the user just taking in a single variadic argument list and parsing it into separate values themselves.

[kschwab]

@jploskey @hramezani I've added support for the above onto #519.