On 2016-12-07 15:33, Ned Batchelder wrote:
On Wednesday, December 7, 2016 at 10:18:32 AM UTC-5, Rustom Mody wrote:
Trying to write some code using sets (well frozen sets)
And was hit by this anomaly
This is the behavior of lists I analogously expect in sets:
>>> []
[]
>>> [[]]
[[]]
>>>
ie the empty list and the list of the empty list are different things
However
(with
f= frozenset
)
>>> f()
frozenset()
>>> f([])
frozenset()
>>> f(f([]))
frozenset()
>>>
The difference is more about the difference between the behavior of a
callable constructor, and a list literal. Lists will behave the same
as frozenset if you use list():
>>> list()
[]
>>> list(list())
[]
>>> list(list(list()))
[]
This is because the constructors can take a sequence, and use those
elements as the new contents. List literals don't work that way.
Spent a good ½ hour finding out this strangeness
And then some figuring out how to get an empty set into a set
This is the best I get:
>>> f([f([])])
frozenset({frozenset()})
That is the way I would have done it also. Or:
>>> s = set()
>>> s.add(frozenset())
>>> frozenset(s)
frozenset([frozenset([])])
Notice the repr output of the result shows how to make it! :)
You must be using Python 2 because on Python 3 I get:
>>> frozenset([frozenset()])
frozenset({frozenset()})
--
https://mail.python.org/mailman/listinfo/python-list
