Hashing within a class

Question

Im trying to hash an object of a custom class using the

hash()

function. My code does the following within the class

def __hash__(self):
    return hash(tuple(self.somelistattribute))

Where the attribute somelistattribute is list of lists such as:

Why do i keep getting an error:

TypeError: unhashable type: 'list'

How do I fix it?

zondo · Accepted Answer · 2016-03-25 19:21:03Z

3

Because list is unhashable, and that includes the sublists. To convert the sublists, use map():

    return hash(tuple(map(tuple, self.somelistattribute)))

answered Mar 25, 2016 at 19:21

zondo

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16 Comments

Randomuser123 Over a year ago

I tried this, I get the same error. I forgot to mention that the it is not a list of lists of integers, but a list os lists of strings. Does that change anything?

zondo Over a year ago

Would you mind giving an example that reproduces the problem?

Randomuser123 Over a year ago

You mean the class constructor? or where I'm specifically encountering the problem?

zondo Over a year ago

I mean the list of lists that can't be pickled. A list of lists of strings when converted to a tuple of tuples of strings doesn't have any lists that can't be pickled. I'd like an example of your list.

Randomuser123 Over a year ago

[["", "", "", "", ""],["", "", "", "", ""],["", "", ".", "", ""], ["", "", "", "", ""],["", "", "", "", ""]]

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Dan Getz · Accepted Answer · 2016-03-25 19:23:17Z

0

The problem is the lists inside of your outer list. Those aren't hashable, and calling tuple() only changes the outer list to a tuple.

You can fix this in a few ways, like with map():

hash(tuple(map(tuple, list_of_lists)))

or with a comprehension:

hash(tuple(tuple(x) for x in list_of_lists))

answered Mar 25, 2016 at 19:23

Dan Getz

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4 Comments

Randomuser123 Over a year ago

I tried this, it doesn't work and i encounter the same problem

Dan Getz Over a year ago

@SrikanthSrinivas then please edit your question to contain code that demonstrates the problem. The code in your question works perfectly fine with the answers you've been given so far.

Dan Getz Over a year ago

@SrikanthSrinivas and that changed nothing; the answers here still work perfectly fine for the example in your question.

zondo Over a year ago

@DanGetz: By the way, the [edit] shortcut link is for the post under which it is used. In this case, your link is for editing your answer.

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