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

"Martin v. Löwis" martin at v.loewis.de
Mon Jan 28 22:54:35 CET 2008

This is why len() is not a method:

map(len, listofstrings)

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 listofstrings] 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

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