TypeError: Unhashable Type 'list'

Why This Happens

Python requires dictionary keys and set elements to be hashable. Since lists can be modified after creation, their hash could change, so Python forbids their use as keys. Tuples, being immutable, are hashable.

The Problem

coords = {[0, 0]: 'origin', [1, 1]: 'point'}

The Fix

coords = {(0, 0): 'origin', (1, 1): 'point'}

Step-by-Step Fix

1. 1

   Find the unhashable object

   Look at the line where you create a dict or set and find where a list is used as a key or element.

2. 2

   Convert to tuple

   Replace the list with tuple(your_list) or use parentheses instead of brackets.

3. 3

   Use frozenset for set-of-sets

   If you need a set containing sets, use frozenset() instead of set().