[Python-Dev] namedtuple implementation grumble

[R. David Murray]

On Fri, 06 Jun 2014 19:50:57 +0100, Chris Withers <chris at simplistix.co.uk> wrote:
> I've been trying to add support for explicit comparison of namedtuples 
> into testfixtures and hit a problem which lead me to read the source and 
> be sad.
> 
> Rather than the mixin and class assembly in the function I expected to 
> find, I'm greeted by an exec of a string.
> 
> Curious as to what lead to that implementation approach? What does it 
> buy that couldn't have been obtained by a mixin providing the functionality?
> 
> In my case, that's somewhat irrelevant, I'm looking to store a comparer 
> in a registry that would get used for all namedtuples, but I have 
> nothing to key that off, there are no shared bases other than object and 
> tuple.
> 
> I guess I could duck-type it based on the _fields attribute but that 
> feels implicit and fragile.
> 
> What do you guys suggest?

I seem to remember a previous discussion that concluded that duck typing
based on _fields was the way to go.  (It's a public API, despite the _,
due to name-tuple's attribute namespacing issues.)

--David