I would love to get this issue resolved; it seems like everyone agrees that it's a bug. It came up for me recently: https://bugs.python.org/issue41047. Judging from the comments above, the consensus is that the relevant line, `self._check_value(action, value)` should either be replaced with something like `if isinstance(value, collections.abc.Sequence): for v in value: self._check_value(action, v)` or be removed entirely.

I think the line should just be removed. I think it's fair to assume that users of `argparse` know what they're doing, so I think they should be allowed to pass default values that conflict with `choices`. Also, removing the line makes the behavior consistent with the optionals, which don't check whether default values are in `choices`. See the below script:

```
import argparse


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--foo", nargs="+", default=[-1], choices=range(10))
    parser.add_argument("--bar", nargs="*", default=-1, choices=range(10))
    parser.add_argument("pos", nargs="?", default=-1, choices=range(10))
    args = parser.parse_args()
    print(args)


if __name__ == '__main__':
    main()
```

Which yields:
```
$ python argparse_test.py 
Namespace(foo=[-1], bar=-1, pos=-1)
```