Keys in dict and keys not in dict

[Peter Otten]

Ben Finney wrote:

> Chris Angelico <rosuav at gmail.com> writes:
> 
>> Sounds like a set operation to me.
>>
>> expected = {"foo", "bar", "spam"}
>> missing = expected - set(json)
> 
> That works (because iterating a dict returns its keys). But it is less
> immediately understandable, IMO, than this::
> 
>     expected = {"foo", "bar", "spam"}
>     missing = expected - set(json.keys())

There's no need to materialize the set of keys: 

>>> expected = {"foo", "bar", "ham"}
>>> json = dict(foo=1, bar=2, spam=3)
>>> expected - json.keys()
{'ham'}

In Python 2 use json.viewkeys() instead of keys().