How to get the difference between two dictionaries in Python?

Solution 1:

I think it's better to use the symmetric difference operation of sets to do that Here is the link to the doc.

>>> dict1 = {1:'donkey', 2:'chicken', 3:'dog'}
>>> dict2 = {1:'donkey', 2:'chimpansee', 4:'chicken'}
>>> set1 = set(dict1.items())
>>> set2 = set(dict2.items())
>>> set1 ^ set2
{(2, 'chimpansee'), (4, 'chicken'), (2, 'chicken'), (3, 'dog')}

It is symmetric because:

>>> set2 ^ set1
{(2, 'chimpansee'), (4, 'chicken'), (2, 'chicken'), (3, 'dog')}

This is not the case when using the difference operator.

>>> set1 - set2
{(2, 'chicken'), (3, 'dog')}
>>> set2 - set1
{(2, 'chimpansee'), (4, 'chicken')}

However it may not be a good idea to convert the resulting set to a dictionary because you may lose information:

>>> dict(set1 ^ set2)
{2: 'chicken', 3: 'dog', 4: 'chicken'}

Solution 2:

Try the following snippet, using a dictionary comprehension:

value = { k : second_dict[k] for k in set(second_dict) - set(first_dict) }

In the above code we find the difference of the keys and then rebuild a dict taking the corresponding values.

Solution 3:

Another solution would be dictdiffer (https://github.com/inveniosoftware/dictdiffer).

import dictdiffer                                          

a_dict = {                                                 
  'a': 'foo',
  'b': 'bar',
  'd': 'barfoo'
}                                                          

b_dict = {                                                 
  'a': 'foo',                                              
  'b': 'BAR',
  'c': 'foobar'
}                                                          

for diff in list(dictdiffer.diff(a_dict, b_dict)):         
    print diff

A diff is a tuple with the type of change, the changed value, and the path to the entry.

('change', 'b', ('bar', 'BAR'))
('add', '', [('c', 'foobar')])
('remove', '', [('d', 'barfoo')])