[Python-Dev] dict contains raises TypeError on unhashable input (original) (raw)

Benjamin Peterson benjamin at python.org
Sat Jul 20 09:13:47 CEST 2013

2013/7/19 Ethan Furman <ethan at stoneleaf.us>:

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.value2membermap: 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.

I'm not exactly sure what the last part of that sentence means.

Anyway, it's well established that operations on a key in a dict are going to involve looking up the key, and thus hashing it. You wouldn't expect, {}.get(unhashable, None) not to raise, right?

-- Regards, Benjamin

More information about the Python-Dev mailing list