Hashing arrays in Python

Question

Is it possible to hash lists?

For example, I know that hashes of tuples are possible:

>>> hash((1,2,3,4,5,6))
-319527650

But is it possible to hash a list?

>>> hash([1,2,3,4,5,6])
hash_value

Possible Solution:

Very in depth explanation to the hashing of lists, here.

Asked By: user1786283

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Source

Answer 1

Python doesn’t allow you to use mutable data as keys in dictionaries, because changes after insertion would make the object un-findable. You can use tuples as keys.

Answered By: Ned Batchelder

Answer 2

Just try it:

>>> hash((1,2,3))
2528502973977326415
>>> hash([1,2,3])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>> hash(frozenset((1,2,3)))
-7699079583225461316
>>> hash(set((1,2,3)))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'

So you can get hash of tuple and frozenset since the are immutable, and you can’t do it for list and set because they are mutable.

Answered By: Roman Bodnarchuk

Answer 3

If you really need to use a list as a dictionary key, try converting it to a string first.
my_list = str(my_list)

Answered By: Ohmless

Answer 4

First you have to convert it to a tuple:

print(hash(tuple([1, 2, 3, 4, 5, 6])))

Answered By: Rufat

Hashing arrays in Python

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