[Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC) (original) (raw)

Paul Moore p.f.moore at gmail.com
Sun Jun 1 15:57:55 CEST 2008

2008/6/1 Guido van Rossum <guido at python.org>:

The case for String has already been made. Actually I'm not sure. One you know that isinstance(x, String) is true, what can you assume you can do with x? [...] Right. I'm now beginning to wonder what exactly you're after here -- saying that something is an "X" without saying anything about an API isn't very useful. You need to have at least some API to be able to do anything with that knowledge.

Apologies to Raymond if I'm putting words into his mouth, but I think it's more about not doing things with the type - a String is a Sequence that we don't wish to iterate through (in the flatten case), so the code winds up looking like

for elem in seq:
    if isinstance(elem, Sequence) and not isinstance(elem, String):
        recurse into the element
    else:
        deal with the element as atomic

This implies that other "empty" abstract types aren't useful, though, as they are not subclasses of anything else...

Paul.

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