[Python-ideas] Introduce collections.Reiterable
Stephen J. Turnbull
stephen at xemacs.org
Fri Sep 20 19:34:58 CEST 2013
Andrew Barnert writes:
> And that makes me think that I (and the people who have been
> responding to you before me) have missed something important in
> this "manually iterable" or "directly iterable" idea. So, maybe you
> should try explaining it a different way?
How about "'Iterable' is a terrible name for an ABC that excludes an
important class of iterables"?
You see, the library manual lies (section 4.5 "Iterator types"):
One method needs to be defined for container objects to provide
But in fact this is contradicted (section 2 "Built-in functions"):
Return an iterator object. The first argument is interpreted very
differently depending on the presence of the second argument. Without
a second argument, object must be a collection object which supports
the iteration protocol (the __iter__() method), or it must support the
sequence protocol (the __getitem__() method with integer arguments
starting at 0).
I suggest that section 4.5 be corrected to
Container objects provide iteration support when either of the methods
container.__iter__() # iteration protocol
container.__getitem__() # sequence protocol
is defined. In the latter case, __getitem__() must accept integer
arguments starting at 0.
Curiously, all of the built-in sequences support both protocols. I
suppose this section ought to say which is preferred.
The net result is that I guess Nick's test needs to be refined to
return isIterable and not isinstance(o, collections.abc.Iterator)
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