[Python-ideas] Method chaining notation

[David Mertz]

On Wed, Feb 26, 2014 at 12:54 PM, Ron Adam <ron3200 at 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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