[Python-Dev] Impact of Namedtuple on startup time

[Tim Peters]

[Giampaolo Rodola' <g.rodola at gmail.com>]
> ....
> To be entirely honest, I'm not even sure why they need to be forcefully
> declared upfront in the first place, instead of just having a first-class
> function (builtin?) written in C:
>
> >>> ntuple(x=1, y=0)
> (x=1, y=0)
>
> ...or even a literal as in:
>
> >>> (x=1, y=0)
> (x=1, y=0)

How do you propose that the resulting object T know that T.x is 1. T.y
is 0, and T.z doesn't make sense?  Declaring a namedtuple up front
allows the _class_ to know that all of its instances map attribute "x"
to index 0 and attribute "y" to index 1.  The instances know nothing
about that on their own, and consume no more memory than a plain
tuple.  If your `ntuple()` returns an object implementing its own
mapping, it loses a primary advantage (0 memory overhead) of
namedtuples.