On Wed, Feb 26, 2014 at 12:54 PM, Ron Adam <ron3200@gmail.com> wrote:

For example you could say, we don't need dict.items because we can do...

zip(dict.keys(), dict.values())

Have we actually been promised that d.keys() and d.values() walk the (unordered) dictionary in the same order, for every Python implementation/version? While I think it is almost certainly true in practice, I haven't where this invariant is guaranteed:

assert [d[k] for k in d] == d.values()

I could trivially subclass dict to make a pretty good dictionary that violated this invariant, e.g.:

class SortedDict(dict):

def keys(self):

return sorted(dict.keys(self))

def values(self):

return sorted(dict.values(self))

I actually don't have great difficulty imagining purposes for which this would be a useful data structure even. Clearly it violates the invariant listed though.

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