The issue is that the set type does not allow a list as an element, due to its rule of no duplicates. As demonstrated by:
foo = {1, 'foo', [1,2,3]}
Traceback (most recent call last):
File "C:\Users\rjmac\Documents\VSCode\Python\atest.py", line 21, in <module>
result = pytest()
File "C:\Users\rjmac\Documents\VSCode\Python\atest.py", line 12, in pytest
foo = {1, 'foo', [1,2,3]}
TypeError: unhashable type: 'list'