<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def mapped(cls, key='id', **kwargs):
 """Create list of instances from a mapping."""

    kwargs.setdefault('metadata', {})
    kwargs['metadata']['jsonldPredicate'] = {'mapSubject': key}
    kwargs.setdefault('default', attr.Factory(list))

    def converter(value):
        """Convert mapping to a list of instances."""
        if isinstance(value, dict):
            result = []
            for k, v in iteritems(value):
                if not hasattr(cls, 'from_cwl'):
                    vv = dict(v)
                    vv[key] = k
                else:
                    vv = attr.evolve(cls.from_cwl(v), **{key: k})
                result.append(vv)
        else:
            result = value

        def fix_keys(data):
            """Fix names of keys."""
            for a in fields(cls):
                a_name = a.name.rstrip('_')
                if a_name in data:
                    yield a.name, data[a_name]

        return [
            cls(**{kk: vv
                   for kk, vv in fix_keys(v)}) if not isinstance(v, cls) else v
            for v in result
        ]

    kwargs['converter'] = converter
    return attr.ib(**kwargs)