def pick_kwargs(kwargs: dict, required_args: list, prefix: str = None):
    picked = {k: v for k, v in kwargs.items() if k in required_args}
    prefixed = {}
    if prefix:
        prefix = prefix + '__'
        prefixed = {
            _remove_prefix(k, prefix): v
            for k, v in kwargs.items()
            if k.startswith(prefix)
            and _remove_prefix(k, prefix) in required_args
        }
    conflicting_args = [k for k in picked if k in prefixed]
    if conflicting_args:
        raise ValueError(
            'Both prefixed and unprefixed args were specified '
            'for the following parameters: {}'.format(conflicting_args)
        )
    return tz.merge(picked, prefixed)