Best solution (Re: Discussion about PEP 234: iterators)

s713221 at student.gu.edu.au s713221 at student.gu.edu.au
Tue Feb 20 12:02:36 CET 2001


Huaiyu Zhu wrote:
> 
> On Mon, 19 Feb 2001 03:32:41 GMT, Jeff Petkau <jpet at eskimo.com> wrote:
> 
> >- make 'dict.keys' return the proxy object, which is
> >  callable.  Make proxy.__call__() return an actual
> >  list from the proxy so dict.keys() works as before.
> >  So cute I'm ashamed I even thought of it.
> 
> What a bright idea!  This is the best solution I've seen so far.  I'm
> surprised no one has commented on this yet.  So let me spell it out to
> generate more interest.
> 
> With this proposal, all of these work as expected
> 
> for k in dict.keys:
> for k, v in dict.items:
> for v in dict.values:
> 
> without creating extra list.  And all of these work as expected
> 
> if k in dict.keys:
> if k, v in dict.items:
> if v in dict.values:
> 
> Only the last need linear search, which is natural.
> 
> There will be no confusion over what 'in' means for dict.  There is no
> clutter of code.  And "explicit is better than implicit".
> 
> Furthermore, all the old codes work as well, like
> 
> a = dict.keys()
> v = dict.values()[3]
> x, y = dict.items()[2]
> 
> Whatever the actual implementation would be, this seems to offer the
> cleanest syntax space for iterators and has_item proxies and so on whenever
> they become available.
> 
> In the actual implementation, all iterators need to provide three magical
> methods: __getitem__, __contains__ and __call__ with the usual sematic
> restrictions:
> 
> __contains__ return true iff __getitem__ will get it at least once.
> __call__ will return a list of objects returned by __getitem__.
> __getitem__ raise IndexError at the end.
> 
> Huaiyu

As long as there aren't any problems unforseen, this gets my vote as
well.

Joal Heagney/AncientHart



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