On 07/20/2013 03:21 AM, Ronald Oussoren wrote:
On 20 Jul, 2013, at 1:47, Ethan Furman <et...@stoneleaf.us> wrote:
While working on issue #18508 I stumbled across this:
Traceback (most recent call last):
...
File "/usr/local/lib/python3.4/enum.py", line 417, in __new__
if value in cls._value2member_map:
TypeError: unhashable type: 'list'
I'll wrap it in a try-except block, but I must admit I was surprised the answer
wasn't False. After all, if the input is unhashable then obviously it's not in
the dict; furthermore, if I were to compare the number 5 with a set() I would
get False, not a TypeMismatch error, and dict keys are basically done by
equality, the hash is just (?) a speed-up.
Not quite, there are some objects that compare equal without both of them being
hashable:
frozenset([1,2]) == set([1,2])
True
dct = { frozenset([1,2]): 1 }
frozenset([1,2]) in dct
True
set([1,2]) in dct
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'
It would be strange if the last test would return False instead of raising an
error.
Yeah, that would be unfortunate.
Okay, I can see dict.__contains__ and friends raising a TypeError, but
what about dict.keys() ? In 2.x it returned a list, in 3.x it returns a
dict_keys, and dict_keys also raises an error instead of returning False.
--
~Ethan~
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
