transforming a list into a string
Christopher T King
squirrel at WPI.EDU
Mon Aug 2 03:16:34 CEST 2004
On Sun, 1 Aug 2004, Tim Peters wrote:
> The difference is that list() creates a concrete list object from its
> argument, but there's no such thing as "a concrete iter object".
You've got me there.
> Iteration is a protocol, not a type. iter(obj) invokes
Only if obj.__iter__() is defined; otherwise it makes something up using
__getitem__ as appropriate.
> and I don't know of any existing __iter__ implementation that returns an
> object that supports slicing.
True. Built-in classes (such as list & tupleiterator) would have to be
extended with this function (trivial if they all subclass from a common
base class). As to user classes, I'm proposing this on the assumption
that a programmer would implement their own __getitem__ (I've been saying
__getslice__ previously, __getitem__ is what I should be saying) if the
functionality is so desired, which can be as trivial as setting
__getitem__=islice, provided islice is extended to accept slice objects.
Though, this would break __getitem__ in the case of getting a single
item (I can see where this is heading)...
> The only thing required of __iter__ is that it return an object that
> supports the iteration protocol (meaning an object that supports next()
> and __iter__() methods). So again, adding the ability to slice too
> would mean requiring more of __iter__ methods -- or changing the
> implementation of iter() to ignore __iter__ methods and make something
> up itself. It's A Visible Change no matter how you cut it.
You've made your point. I guess this will just have to go on the "it
would be neat if it worked this way, but it just doesn't" list for now ;)
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