Get differences between two lists of dictonaries (result as two differences lists) in Python - this is a draft for a question which finally landed here: https://stackoverflow.com/questions/68091970/get-differences-between-two-lists-of-dictionaries-result-as-two-differences-lis

stack question.md

I have two lists of dictonaries. They contain gmail labels and filters. I need to get differences between them in form of two differences lists. I want order of the elements to be preserved.

Example:

a=[
	{'name': 'label_a'},
	{'color': {'background': '#42d692', 'text': '#094228'}, 'name': 'label_b'},
	{'name': 'label_d'},
	{'name': 'label_e'},
]

b=[
	{'name': 'label_a'},
	{'name': 'label_b'},
	{'name': 'label_c'},
	{'name': 'label_d'},
]

Expected results:

a_diff=[
	{'color': {'background': '#42d692', 'text': '#094228'}, 'name': 'label_b'},
	{'name': 'label_e'},
]

b_diff=[
	{'name': 'label_b'},
	{'name': 'label_c'},
]

This is how I could do this, but I think it might be inefficient. Can I do something better?

a_diff=[]
b_diff=[]

for i in a:
    if i not in b:
        a_diff.append(i)

for j in b:
    if j not in a:
        b_diff.append(j)

I don't need to keep original lists after this operation, so this can be in-place. Speed is most important. So this question can be also rephrased as: "How to remove common elements between two lists from those lists?"

When you provide solution, let know if it would work also on any two lists or only lists of dictonaries.

Also please let know if your solution will remove duplicates or not (I am interested in both kinds of solutions):

a=[
	{'name': 'label_a'},
	{'name': 'label_a'},
	{'name': 'label_b'},
]

b=[
	{'name': 'label_a'},
	{'name': 'label_b'},
	{'name': 'label_c'},
]

Results with removed duplicate.

a_diff=[
]

b_diff=[
	{'name': 'label_c'},
]

Results without removed duplicate.

a_diff=[
	{'name': 'label_a'},
]

b_diff=[
	{'name': 'label_c'},
]

Hi, just in case you are still interested in a possible solution:

For the case with removed duplicates you can make use of sets:

def get_diff(a, b):
    # convert dicts to strings and lists to sets
    # converting dicts to strings is required since dicts are not hashable, so a list of dicts can not be converted to a set of dicts
    a = {json.dumps(item, sort_keys=True) for item in a}
    b = {json.dumps(item, sort_keys=True) for item in b}

    # get differences    
    a_diff = a - b
    b_diff = b - a

    # convert strings back to dicts and set back to list
    a_diff = [json.loads(item) for item in a_diff]
    b_diff = [json.loads(item) for item in b_diff]
    return a_diff, b_diff 

I did not test the run-time, but I would expect this method to be faster for long lists and small dicts.
I hope this helps!

@MoritzPlenz

Thanks.

This question was posted (after modifications) on SO: https://stackoverflow.com/questions/68091970/get-differences-between-two-lists-of-dictionaries-result-as-two-differences-lis
I updated description of this gist to make it clear.

If you want, you can post your solution as another answer.

In that case sorry for the spam.
The answers on SO look good, so I won't copy my answer there.