Error when parsing empty list with subcast

[sabdouni]

Hello,

The env.list can't handle an empty list when using subcast
It raises an exception environs.EnvValidationError: Environment variable "LIST" invalid: {0: ['Not a valid integer.']}
This can be reproduced by e.g

    os.environ["LIST"] = ""
    env = Env()
    LIST = env.list("LIST", [], subcast=int)

If you don't use subcast it works just fine by e.g

    os.environ["LIST"] = ""
    env = Env()
    LIST = env.list("LIST", [])

Maybe one solution is if the env variable is falsy (empty or doesn't exist) env.list should return the default value if defined

Happy to submit a PR if that would be of interest. Thanks!

[sloria]

Thanks for reporting. PRs welcome! =)

[sabdouni]

@sloria
The bug is located in the method _preprocess_list and is not really related to environs code but to a really weird behavior of 'split' see here

I have a fix :

• Refactor _preprocess_list to this :

def _preprocess_list(value: typing.Union[str, typing.Iterable], **kwargs) -> typing.Iterable:
    if ma.utils.is_iterable_but_not_string(value):
        return value
    return typing.cast(str, value).split(",") if value != "" else []

• And add this unit test :

    def test_list_with_empty_env_and_subcast(self, set_env, env):
        set_env({"LIST": ""})
        assert env.list("LIST", subcast=int) == []
        assert env.list("LIST", subcast=float) == []

What do you think ?

[sloria]

Seems like a reasonable fix

[sloria]

Fix is released in 7.3.1