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 not
nearly as efficiently as reusing the argument parsing machinery as in
the 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 cls
David
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