Python TypeError: unhashable type: 'list'

Question

I'm trying to run a program which is effectively doing the following:

if [4, 5, False, False, False, False] in {}

And, on this line, I'm getting a TypeError: unhashable type 'list'

What am I doing wrong?

I have data structures that look something along the lines of [4,5,False,False,False,False] and I want to find them within an unordered list of items. {} was an example (that my code happened to be failing on at the time) of such a thing. I'm now using a list instead of a dictionary, and it's working out better. — River Tam
– River Tam, Commented Feb 7, 2013 at 15:13

gerrit · Accepted Answer · 2013-02-07 14:37:30Z

5

The code if foo in {} checks if any of the keys of the dictionary is equal to foo.

In your example, foo is a list. A list is an unhashable type, and cannot be the key of a dictionary.

If you want to check if any entry of a list is contained in a dictionaries' keys or in a set, you can try:

if any([x in {} for x in (4, 5, False)]).

If you want to check if any of your values is equal to your list, you can try:

if any([v == [4, 5, False, False, False, False] for v in your_dict.values()])

edited Feb 7, 2013 at 14:37

answered Feb 7, 2013 at 14:30

gerrit

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Comments

kamae · Accepted Answer · 2013-02-07 14:37:19Z

1

A set holds hashable objects, which means that they are sortable and it enables efficient search/insert method. On the other hand a list is not hashable. That's why your code makes error. I recommend to use tuple instead of list.

if (4, 5, False, False, False, False) in {}:
  ...

answered Feb 7, 2013 at 14:37

kamae

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2 Comments

gerrit Over a year ago

This is still more efficiently written as if False:. It would be more useful if the OP told us what s/he really wants to achieve.

gleb.pitsevich Over a year ago

Thanks for noticing that tuples can be used as dictionary keys instead of lists.

Yevgen Yampolskiy · Accepted Answer · 2013-02-07 14:33:46Z

0

You can do something like

if all(x in {} for x in [4, 5, False, False, False, False]):
    ....

or

if any(x in {} for x in [4, 5, False, False, False, False]):
    ....

depending on what you want

answered Feb 7, 2013 at 14:33

Yevgen Yampolskiy

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3 Comments

gerrit Over a year ago

any(x in {} for x in [4, 5, False]) returns True. I was surprised by this, I guess any considers the iterable as a whole, and an iterator is true. So it should be any([x in {} for x in [4, 5, False]]).

Janne Karila Over a year ago

@gerrit any(x in {} for x in [4, 5, False]) returns False for me, both in Python 2.7 and 3.3

gerrit Over a year ago

@JanneKarila Aah! I was using pylab, which does from numpy import *. numpys any is shadowing the builtin any.

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