#9 most askedVery commonMediumData types & mutability

How do dicts and sets work?

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Why are dict lookups O(1)? What can be a dict key or set member?

🔮 Predict the output

seen = set()
seen.add((1, 2))
try:
    seen.add([1, 2])
except TypeError as e:
    print("error:", e)
print((1, 2) in seen, len({1: "a", 1.0: "b", True: "c"}))

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