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[Python-Dev] namedtuple implementation grumble

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On Sun, Jun 08, 2014 at 05:27:41PM -0400, Eric V. Smith wrote:> How would you write _Namedtuple.__new__?Knew something must be missing :)  Obviously it's possible, but notnearly as efficiently as reusing the argument parsing machinery as inthe original implementation.I guess especially the kwargs implementation below would suck..    _undef = object()    class _NamedTuple(...):        def __new__(cls, *a, **kw):            if kw:                a = list(a) + ([_undef] * (len(self._fields)-len(a)))                for k, v in kw.iteritems():                    i = cls._name_id_map[k]                    if a[i] is not _undef:                        raise TypeError(...)                    a[i] = v                if _undef not in a:                    return tuple.__new__(cls, a)                raise TypeError(...)            else:                if len(a) == len(self._fields):                    return tuple.__new__(cls, a)                raise TypeError(...)    def namedtuple(name, fields):        fields = fields.split()        cls = type(name, (_NamedTuple,), {            '_fields': fields,            '_name_id_map': {k: i for i, k in enumerate(fields)}        })        for i, field_name in enumerate(fields):            getter = functools.partial(_NamedTuple.__getitem__, i)            setattr(cls, field_name, property(getter))        return clsDavid

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