pythonintermediate10 minutes

Predict the Output of a Nested List and Dictionary Manipulation

Analyze the given Python code that manipulates nested lists and dictionaries, and predict its exact printed output.

Challenge prompt

Examine the provided Python code snippet carefully. The code defines nested lists and dictionaries, modifies some values, and prints results after these changes. Your task is to determine exactly what the output will be when this code runs.

Guidance

• Follow the flow of the code step-by-step, focusing on how lists and dictionaries are modified.
• Keep track of variable references, especially how changes to one object affect others that reference the same object.

Hints

• Remember that lists and dictionaries are mutable objects and assignments can create references, not copies.
• Look closely at the order of operations—the modifications after initializations affect later prints.

Starter code

data = [{'a': [1, 2, 3]}, {'b': [4, 5]}]
ref = data[0]['a']
ref.append(4)
data[1]['b'] = ref
print(data)
print(ref)

Expected output

[{'a': [1, 2, 3, 4]}, {'b': [1, 2, 3, 4]}] [1, 2, 3, 4]

Core concepts

mutable objectslist and dictionary referencesobject mutation

Challenge a Friend

Send this duel to someone else and see if they can solve it.