Pickle - Unable to correctly store appended dictionary to list

Question

I am trying to save a list of multiple dictionaries in a pickle file and by able at any time to store a new appended dictionary in the list and save it in the pickle file and then load the pickle file as a list of dictionaries. So far, the code behaves as follows:

The first time I try to append a dictionary in the list, the pickle file looks like this (the data is saved succesfully):

Running info()......

===================================================
Existing data: []
===================================================

Running save_score()......

Inside try: {}
============================================
Existing data: [{}]
New data: {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}
Saved Data: [{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]
===================================================

The second time I try to append a dictionary in the list, the pickle file looks like this:

Running info()......

===================================================
Existing data: [[{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]]
===================================================

Running save_score()......

Inside try: [{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]
============================================
Existing data: [[{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}], [{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]]
New data: {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}
Saved Data: [[{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}], [{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}], {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]
===================================================

As you can see (the values in the dictionary are not a concern in the example above), instead of appending to the existing list, everytime, a new list inside the list is created. So far, I have not managed to fix this and get the expected output.

The expected output should be:

Saved Data: [{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}, {}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]

Instead, the output is:

Saved Data: [[{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}], [{}, {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}], {'ComputerName': 'computer name', 'PlayerName': 'user 1', 'ComputerScore': 3, 'PlayerScore': 1}]

Code is as follows:

import pickle

data = []
computer_name = "computer name"
username = "user 1"
computer_score = 3
human_score = 1

def save_score():
    try:
        existing_data = pickle.load(open("w6_project.p", "rb"))
        print("Inside try: {}".format(existing_data))
        data.append(existing_data)
    except (OSError, IOError) as e:
        pickle.dump({}, open("w6_project.p", "wb"))
    new_data = {"ComputerName": computer_name, "PlayerName": username, "ComputerScore": computer_score, "PlayerScore": human_score}
    print("============================================")
    print("Existing data: {}".format(data))
    data.append(new_data)
    print("New data: {}".format(new_data))
    pickle.dump(data, open("w6_project.p", "wb"))  # Save the data into a pickle file
    print("Saved Data: {}".format(data))
    print("===================================================")
    pass

def info():
    try:
        existing_data = pickle.load(open("w6_project.p", "rb"))
        data.append(existing_data)
    except (OSError, IOError) as e:
        pickle.dump({}, open("w6_project.p", "wb"))
    print("===================================================")
    print("Existing data: {}".format(data))
    print("===================================================")
    pass

def main():
    print("Running info()......\n")
    info()
    print("\nRunning save_score()......\n")
    save_score()

if __name__ == "__main__":
    main()

Answer 1

Problem is that you have two lists - data and existing_data - and you join them in wrong way. Using append() you put one list inside another list. You should use extend() to join them

 data.extend(existing_data)

or shorter

 data += existing_data

But if you add new data after loading pickle then you should simply assing directly to variable

 data = pickle.load(...)

---

EDIT: Minimal working example

import pickle

computer_name = "computer name"
username = "user 1"
computer_score = 3
human_score = 1

def save_score():
    
    try:
        data = pickle.load(open("w6_project.p", "rb"))
        print("Inside try: {}".format(data))
    except (OSError, IOError) as e:
        data = []
        
    new_data = {"ComputerName": computer_name, "PlayerName": username, "ComputerScore": computer_score, "PlayerScore": human_score}
    data.append(new_data)

    pickle.dump(data, open("w6_project.p", "wb"))  # Save the data into a pickle file

    print("============================================")
    print("Existing Data: {}".format(data))
    print("New Data: {}".format(new_data))
    print("Saved Data: {}".format(data))
    print("Length Data: {}".format( len(data) ))
    print("===================================================")

def info():
    try:
        data = pickle.load(open("w6_project.p", "rb"))
    except (OSError, IOError) as e:
        data = []
        
    print("===================================================")
    print("Existing Data: {}".format(data))
    print("Length Data: {}".format( len(data) ))
    print("===================================================")

def main():
    print("Running info()......\n")
    info()

    print("\nRunning save_score()......\n")
    save_score()

if __name__ == "__main__":
    main()