Comparing 2 codes in python dictionaries

Question

In this code we receive ERROR because dictionaries logic says keys should be immutable
https://code.sololearn.com/c73rDnjoI6VC/?ref=app

I thought in this code we should receive ERROR with same reason
https://code.sololearn.com/cMjC1Q1Bqkgy/?ref=app

As a key in dictionaries 1 in first code has difference to 1 in second code ?
exactly why ?

Answer 1

The error is not about keys having to be immutable. It's about the key being not hashable.

Most objects define a hash function, which returns a unique value for each object. That hash function is used for keys of a dictionary, which is essentially a hashtable.

A list doesn't support hashing. The list elements can be hashed, but not the list itself. That's why you can't use a list as the key.