CODEWITHSUNDEEP
c++pythonhash
kamushin
kamushin

Reputation: 139

How to make a list as a key of dict in Python?

In C++, I will wirte map<vector<int>,int> mv; But in Python,I get a error of "TypeError: unhashable type: 'list'" I guess maybe in C++,map is a red-black tree ,but in Python,the dict is a hash table. But how can I do the same thing like above in Python ?

Upvotes: 1

Views: 112

Answers (2)

Sean Vieira
Sean Vieira

Reputation: 160073

As long as you don't need to resize the key, a tuple would probably be the most efficient way to go about it:

mv = {}
mv[(1, 2, 3)] = 456

Upvotes: 1

falsetru
falsetru

Reputation: 369444

You cannot use list as dictionary key because it is not hashable.

>>> mv = {}
>>> mv[[1,2,3]] = 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

Use tuple instead.

>>> mv[(1,2,3)] = 2
>>> mv
{(1, 2, 3): 2}

Upvotes: 3

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