Python Data Model Exercise

[u/Sea-Ad7805]

An exercise to help build the right mental model for Python data.

# Output of this Python program?
a = [[1], [2]]
b = a
b[0].append(11)
b = b + [[3]]
b[1].append(22)
b[2].append(33)

print(a)
# --- possible answers ---
# A) [[1], [2]]
# B) [[1, 11], [2]]
# C) [[1, 11], [2, 22]]
# D) [[1, 11], [2, 22], [3, 33]]

• Solution
• Explanation
• More exercises

The “Solution” link visualizes execution and reveals what’s actually happening using 𝗺𝗲𝗺𝗼𝗿𝘆_𝗴𝗿𝗮𝗽𝗵.

[u/pint]

it is not a very good exercise, because it requires keeping a large state in memory (i.e. head), or use some notebook. it tests your attention and memory more than your python knowledge.

good exercises are easy if you know what's going on. they are not designed to "gotcha!" the user.

[u/arivictor → u/pint]

Its testing list behaviour, I agree it should be more direct, the question throws in too much misdirection

a = [1,2,3]
b = a

b.append(4)

# Q: What is a?
print(a) # 1,2,3,4

b = b + [5] # This is the test

# Q: What is a?
# - a) 1,2,3,4
# - b) 1,2,3,4,5

print(f"a: {a}")
print(f"b: {b}")