Using non-hashable Python objects as keys in dictionaries

Question

Python doesn\'t allow non-hashable objects to be used as keys in other dictionaries. As pointed out by Andrey Vlasovskikh, there is a nice workaround for the special case of

Answer 1

If you really must, make your objects hashable. Subclass whatever you want to put in as a key, and provide a __hash__ function which returns an unique key to this object.

To illustrate:

>>> ("a",).__hash__()
986073539
>>> {'a': 'b'}.__hash__()
Traceback (most recent call last):
  File "", line 1, in 
TypeError: 'NoneType' object is not callable

If your hash is not unique enough you will get collisions. May be slow as well.