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Python – list of lists – check if unique combination of values has last different value in the list

May 9, 2023

we have a list of lists

links_list = [['project1','repo1', 'folder1', 'target1', 'link1', 'branch1'], 
             ['project1', 'repo1', 'folder1', 'target1', 'link1', 'branch1'], 
             ['project1', 'repo1', 'folder1', 'target1', 'link1', 'branch2'],
             ['project2', 'repo2', 'folder2', 'target2', 'link2', 'branch2']]

for link_list in links_list:
    print(link_list)

Our unique combination of columns are: project, repo, folder and target

That means, it is OK if we have lists which are repeated such as the first two lists:

['project1', 'repo1', 'folder1', 'target1', 'link1', 'branch1'], 
['project1', 'repo1', 'folder1', 'target1', 'link1', 'branch1']

That is not an issue.

it is NOT OK if BRANCH column (the last column) is different for this combination of the first 4 columns: project, repo, folder and target.

So since we have

['project1', 'repo1', 'folder1', 'target1', 'link1', 'branch1'] and

['project1', 'repo1', 'folder1', 'target1', 'link1', 'branch2']
we do not know which BRANCH value is valid so script should exit and throw exception for this use case because for combination:
‘project1’, ‘repo1’, ‘folder1’, ‘target1’ we have two branches: branch1 and branch2 which makes inconsistency.

Link column (column5 – index4) is irrelevant for the logic.

I am really not sure how to start here.

Thanks a lot

>Solution :

combos = {}
for link_list in links_list:
  key = tuple(link_list[:4])
  branch = link_list[5]
  if combos.setdefault(key, branch) != branch:
    raise Exception(f"{key} already has branch '{combos[key]}'.")

You can use setdefault to set and/or retrieve the existing key.