Musings about Python syntax

[Gordon McMillan]

[Jim Althoff]
> Where can one find out more info on
> "hasinterface" and "as_sequence"?

[the eff-bot]
> >    def len(obj):
> >        if hasinterface(obj, as_sequence):
> >            return obj.sequence_length()
> >        if hasinterface(obj, as_mapping):
> >            return obj.mapping_length()
> >        raise TypeError, "len() of unsized object"
> >
> >which, for my non-purist eyes, surely looks as if
> >Python treats "obj" as an arbitrary object.

Didn't you snip the bit about it being psuedo-code?

What the eff-bot is alluding to is a call in the abstract level of 
the C API, which checks whether the type-as-sequence slot in 
the type object is non-NULL. For C types implementing the 
sequence methods, this works. Unfortunately, a Python class 
emulating a sequence will fail this check.

The types SIG was very actively debating this and similar 
topics, until someone posted some code implementing an 
interface protocol. All subsequent attempts at reviving the SIG 
have failed miserably.

and-the-pathologist-who-did-the-autopsy-died-too-ly y'rs


- Gordon