[Python-Dev] NamedTuple (was: Py2.6 ideas)

[python at rcn.com]

[Raymond Hettinger]
> The constructor signature ... Point(*fetchall(s)),
> and it allows for direct construction with Point(2,3) without 
> the slower and weirder form: Point((2,3)).

[Jim Jewett]
>> If you were starting from scratch, I would agree
>> whole-heartedly; this is one of my most frequent 
>> mistakes.The question is whether it makes sense to
>> "fix" NamedTuple without also fixing regular tuple, list, 

Yes.  Tuples and lists both have syntactic support for direct construction and NamedTuples aspire to that functionality:

vec = (dx*3.0, dy*dx/dz, dz)         # Regular tuple
vec = Vector(dx*3.0, dy*dx/dz, dz)   # Named tuple

I've worked with the current version of the recipe for a long time and after a while the wisdom of the signature becomes self-evident.  We REALLY don't want: 
    vec = Vector((dx*3.0, dy*dx/dz, dz))  # yuck
For conversion from other iterables, it is REALLY easy to write:
    vec = Vector(*partial_derivatives)

Remember, list() and tuple() are typically used as casts, not as direct constructors.  How often do you write:
    dlist = list((dx*3.0, dy*dx/dz, dz))
That is usually written:
    dlist = [dx*3.0, dy*dx/dz, dz]
I think the Vec((dx, dy, dz)) sysntax falls into the category of foolish consistency.

Raymond