Is it intentional that the second assertion in the following code fails?

```
from collections import OrderedDict

d = dict(C='carbon')
o = OrderedDict(d)
assert d == o
assert d.viewitems() == o.viewitems()
```

Since d == o, I'm surprised that d.viewitems() != o.viewitems(). If that's intentional, I'd love to understand the rationale.

Note: I hit this while testing a library I authored, https://pypi.python.org/pypi/bidict, which provides a https://en.wikipedia.org/wiki/Bidirectional_map implementation for Python, so I'm especially keen to understand all the subtleties in this area.

Thanks in advance.

This question looks similar to:

Should list compare equal to set when the items are equal?

This looks like a bug in Python 2.7:

# Python2.7
>>> from collections import Set
>>> isinstance({1:2}.viewitems(), Set)
False

# Python3.5
>>> from collections import Set
>>> isinstance({1:2}.items(), Set)
True

I think the dictitems object needs to be registered as a Set.

The fix looks something like this:

diff --git a/Lib/_abcoll.py b/Lib/_abcoll.py
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -473,6 +473,7 @@
         for key in self._mapping:
             yield (key, self._mapping[key])
 
+ItemsView.register(type({}.viewitems()))

Will add a more thorough patch with tests later.

I don't know if it is worth to backport this feature (dict views were registered in 1f024a95e9d9), but the patch itself LGTM. I think tests should be foreported to 3.x (if they don't exist in 3.x).

Are there generic set tests similar to mapping_tests and seq_tests?

New changeset 9213c70c67d2 by Raymond Hettinger in branch '2.7':
Issue #24286: Register dict views with the MappingView ABCs.
https://hg.python.org/cpython/rev/9213c70c67d2

New changeset ff8b603ee51e by Raymond Hettinger in branch 'default':
Issue #24286:  Forward port dict view abstract base class tests.
https://hg.python.org/cpython/rev/ff8b603ee51e

> I don't know if it is worth to backport this feature 

I don't think so either.  The Iterator registry is a bit of a waste.


> Are there generic set tests similar to mapping_tests and seq_tests?

Not that I know of.  Also, I don't see the need.