The issue is that tuples are immutable, and lists are not. Consider the following
d = {}
li = [1,2,3]
d[li] = 5
li.append(4)
What should d[li]
return? Is it the same list? How about d[[1,2,3]]
? It has the same values, but is a different list?
Ultimately, there is no satisfactory answer. For example, if the only key that works is the original key, then if you have no reference to that key, you can never again access the value. With every other allowed key, you can construct a key without a reference to the original.
If both of my suggestions work, then you have very different keys that return the same value, which is more than a little surprising. If only the original contents work, then your key will quickly go bad, since lists are made to be modified.