dict.keys() does not behave as set

[jdts]

I was surprised that the keys of a dict are not treated as an &'able set in µPy:

Code: Select all

>>> d={"foo":1,"bar":2,"baz":3}
>>> type(d.keys())
<class 'dict_view'>
>>> d.keys() & {'baz','foo','faz'}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported types for __and__: 'dict_view', 'set'

vs. CPython3:

Code: Select all

>>> d={"foo":1,"bar":2,"baz":3}
>>> type(d.keys())
<class 'dict_keys'>
>>> d.keys() & {'baz','foo','faz'}
{'foo', 'baz'}

Is this a known limitation of the dict_view class?

[jimmo]

Is this a known limitation of the dict_view class?

Yes, there's a comment in the code "// only supported for the 'keys' kind until sets and dicts are refactored" however to really be classed as a "known limitation" it should have a corresponding test in tests/cpydiff which is what's used to generated the "Differences from CPython" section of the docs.

I can see why this wasn't supported initially (it's very easy to implement but would add code size overhead), but as the comment suggests, a refactoring might make it possible to achieve this with minimal code overhead. I'll raise a bug for the cpydiff test.

[jimmo]

https://github.com/micropython/micropython/issues/5493

[jdts]

Thanks. I checked the known diffs and didn't see anything relevant.

[Damien]

This difference has been added to the CPython-difference part of the docs (see github for reference).