Question

In Python, the only difference between a list and a tuple that I know of is “lists are mutable but tuples are not”. But as far as I believe, it depends on whether the coder wants to risk mutability or not.

So I was wondering whether there are any cases where the use of a tuple over a list is a must. Things that can not be done with a list but can be done with a tuple?

Answer 1

You can use tuples as keys in dictionaries and insert tuples into sets:

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

Which is basically a result of a tuple being hashable while a list isn’t:

>>> hash(list())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>> hash(tuple())
3527539