On 18/02/13 14:53, Oscar Benjamin wrote:
> On 18 February 2013 14:23, John Reid <j.r...@mail.cryst.bbk.ac.uk> wrote:
> [snip]
>> That said it would be nice to know the rationale for
>> namedtuple.__new__ to have a different signature to tuple.__new__. I'm
>> guessing namedtuple._make has a similar interface to tuple.__new__. Does
>> anyone know what the rationale was for this design?
>
> Because namedtuples use names for the arguments in the constructor:
>
>>>> from collections import namedtuple
>>>> Point = namedtuple('Point', 'x y')
>>>> p1 = Point(x=2, y=3)
>>>> p1
> Point(x=2, y=3)
>>>> p1.x
> 2
>
That's a good point. I haven't used __new__ much before but wouldn't
something like this __new__() cater for both uses? (Example taken from
namedtuple docs
http://docs.python.org/2/library/collections.html#collections.namedtuple).
>>> Point = namedtuple('Point', ['x', 'y'], verbose=True)
class Point(tuple):
'Point(x, y)'
__slots__ = ()
_fields = ('x', 'y')
def __new__(_cls, *args, **kwds):
'Create a new instance of Point(x, y)'
if args:
return _tuple.__new__(_cls, args)
else:
return _tuple.__new__(_cls, (kwds[f] for f in _fields))
...
Perhaps I could subclass namedtuple so that my namedtuples have the
correct signature for __new__.
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