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TypeError: unhashable type: 'list'

What it means

You used a list as a dictionary key or as an item in a set. Python stores keys and set items by a hash worked out from their contents, and a list can change, so it has no hash. Use a tuple instead; dictionaries and sets can change too, and give the same error with 'dict' or 'set'.

1. A list as a dictionary key

This raises the error

Broken
places = {}
point = [3, 4]
places[point] = 'home'
print(places)
Output
Traceback (most recent call last):
  File "<exec>", line 3, in <module>
TypeError: unhashable type: 'list'

The fix

Fixed
places = {}
point = (3, 4) # a tuple cannot change, so it can be a key
places[point] = 'home'
print(places)
print(places[(3, 4)])
Output
{(3, 4): 'home'}
home

A tuple is like a list that cannot be changed, so Python can hash it. Use tuple(my_list) to convert a list you already have.

Try fixing it yourself in the editor

2. Putting lists in a set to remove duplicates

This raises the error

Broken
pairs = [[1, 2], [3, 4], [1, 2]]
unique = set(pairs)
print(unique)
Output
Traceback (most recent call last):
  File "<exec>", line 2, in <module>
TypeError: unhashable type: 'list'

The fix

Fixed
pairs = [[1, 2], [3, 4], [1, 2]]
unique = set(tuple(p) for p in pairs)
print(unique)
print(len(unique), 'unique pairs')
Output
{(1, 2), (3, 4)}
2 unique pairs

Each inner list becomes a tuple, and tuples can go in a set. Convert back with [list(p) for p in unique] if you need lists again.

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3. A dictionary inside a set

This raises the error

Broken
seen = set()
seen.add({'id': 7, 'name': 'Ana'})
print(seen)
Output
Traceback (most recent call last):
  File "<exec>", line 2, in <module>
TypeError: unhashable type: 'dict'

The fix

Fixed
seen = set()
user = {'id': 7, 'name': 'Ana'}
seen.add(user['id']) # store something that cannot change, like the id
print(seen)
print(7 in seen)
Output
{7}
True

A dictionary can change, so it cannot go in a set either. Store a simple value that identifies it, such as an id, or keep the dictionaries in a list.

Try fixing it yourself in the editor

When you see this error, check

  • Look at the dictionary key or set item on the failing line and print its type().
  • Convert a list to a tuple with tuple() before using it as a key.
  • Use frozenset() when you need a set inside a set or as a key.
  • Remember that {[1, 2]} is a set, so it also tries to hash the list.

Related errors

All Python errors · How to read a traceback · Step through your code