Python either. I correct my post above to switch to indexing by a tuple, because what I originally had is wrong:

    >>> d = {}
    >>> d[[1,2]] = 10
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: unhashable type: 'list'

This is why I qualified my statement with "Each has their own take on the problem of being unable to use mutable keys,".

Go can be consistent in a simple way because of its type system, it can see if any part of a key has something in it that can't be hashed: https://play.golang.org/p/rf8IqPb76Em

Python, as befits Python, has default behavior for instances that I believe is "is" equivalency, but you can override that with various double-underscore methods to do whatever.