[Python-Dev] functions vs methods (was Re: trunc())

["Martin v. Löwis"]

> This is why len() is not a method:
> 
>     map(len, list_of_strings)

That's a good use case - but is that the reason?

I would think that the true historical reason is that when len()
was introduced, there weren't methods in the language. And even
when support for methods was added, many types supporting len wouldn't
easily support methods (e.g. the string type).

> What I don't know is to what extent this argument still holds in the
> presence of listcomps and genexps:
> 
>     [s.len() for s in list_of_strings]
> 
> However, you still need ``len`` as a function to pass around as a
> callback in other cases where you need a generic function because the
> type of your data is not predetermined.

You don't *need* it for that; you could also pass around
lambda x:x.len()

It's clear that you need functions for a functional programming style.
However, I would question that typical Python code is inherently
functional, and instead I believe that it could just as well or better
be object-oriented - it's just that Python mandates functions at certain
places.

> In any event, I consider dropping len() from builtins to be gratuitous
> breakage, even in 3.0.

I wouldn't want to propose removal of len(), no. However, I do think
that adding more builtins (trunc in particular) is bad, especially
when they make perfect methods.

Regards,
Martin