Python list overwritten each time the previous items

Question

The objective of my application is to create a copy of documents and insert them into the database for each annotator, for example, let's say the master user has 3 documents and two annotators, let's say the first annotator has the email [email protected] and the second one has the email [email protected], finally, I need to insert in the database 3 documents for [email protected] and 3 other documents for [email protected]. So to do this, I created first a list containing the copy of documents, and I didn’t assign the annotator

 created_documents_in_iaa = []
    created_documents_in_iaa += [DocumentIAATask(
                    name=document.name,
                    spans=document.spans,
                    entity=document.entity,
                    original_document=document,
                    IAA_Task=iaa_task) for document in all_documents_in_iaa.iterator(chunk_size=1)]

And after that, I added an annotator to each document, and I append each modified created_documents_in_iaa list to the tsks_list:

    tasks_list = []
    for user in users_instance_list:
        try:
            for i in range(len(created_documents_in_iaa)):
                created_documents_in_iaa[i].annotator = user

            tasks_list.append(created_documents_in_iaa)

        except Exception as e: 
            print(e)

Finally, I created a copy of documents in the PostgreSQL database:

for task in tasks_list:
    DocumentIAATask.objects.bulk_create(task)

However, in the result, I found 6 documents inside the table of the first annotator, and nothing for the other one, after I debugged the code, I found that tasks_list overwritten each time the list, that's means when I add the first annotator to the 3 documents, and when I did the same for the other annotator, the list overwritten the previous one, that's means, I found in the tasks_list 2 objects, each object contains 3 documents, and each document contains the same annotator, so the other one was changed after the append. I tried to fix this problem using some similar problems that I found them on the net:

1. tasks_list.append(created_documents_in_iaa[:])

2. tasks_list.append(created_documents_in_iaa.copy())

tasks_list2 += tasks_list2[:] + created_documents_in_iaa tasks_list.append(tasks_list2)

However, it's still the same problem. Any suggestion, please?