Unordered hash in Python

Question

I'd like to compare the dicts by content, so I thought this can be done by creating an unordered hash of the item tuples.

What is the most elegant solution for that?

I was thinking about XORing all individual hashes, but maybe there is another ready-made solution?

EDIT: I have nested data structures. Some classes contain dicts. These classes can be aggregated to sets. So to compare the sets with the predefined set comparison I have to implement both __eq__ (which is easy) and __hash__ (which is my question) for my dict-classes?!

I do not follow what you are trying to do. Could you give us some examples of comparisons you want to make? — Martijn Pieters
– Martijn Pieters, Commented Sep 25, 2012 at 9:59
Possible duplicate of stackoverflow.com/questions/1165352/… ? — Hans Then
– Hans Then, Commented Sep 25, 2012 at 10:06
Are your classes immutable? set assumes the hash values of the elements do not change. — Janne Karila
– Janne Karila, Commented Sep 25, 2012 at 11:40
@JanneKarila: Hmm, they aren't exactly immutable, but I only need the set comparison momentarily to compare an unordered set of my classes. — Gere
– Gere, Commented Sep 25, 2012 at 12:06

Jon Clements · Accepted Answer · 2012-09-25 10:45:06Z

2

To check that all values are the same for overlapping keys, one of the following (depending on Python version) and style:

if all(dict_a[key] == dict_b[key] for key in dict_a.viewkeys() & dict_b.viewkeys())

if all(dict_a[key] == dict_b[key] for key in set(dict_a) & set(dict_b))

To handle the "are they the same value" a bit more specifically...

for k, v in dict_a.iteritems():
    try:
        ov = dict_b[k]
    except KeyError as e:
        continue
    if v == ov: 
        pass # or whatever

edited Sep 25, 2012 at 10:45

answered Sep 25, 2012 at 10:30

Jon Clements

143k34 gold badges254 silver badges288 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jon Clements Over a year ago

@BurhanKhalid That's what is being used in the 2nd example - the first example is taking advantage of the dict_keys object (which can behave set-ish ) returned by .viewkeys() - so not quite sure what your comment means?

Rohit Jain · Accepted Answer · 2012-09-25 10:18:08Z

0

See documentation for Mapping Type.. You have already got operators defined to do various operations on Dictionary..

answered Sep 25, 2012 at 10:18

Rohit Jain

214k45 gold badges419 silver badges534 bronze badges

Collectives™ on Stack Overflow

Unordered hash in Python

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related