Dictionaries

Key–value maps with fast lookup — ideal for configurations, counters and JSON data.

Beginner

resistors = {"R1": 220, "R2": 10_000}
resistors["R3"] = 4_700            # add
resistors.get("R9", 0)              # default if missing
for name, ohms in resistors.items():
    print(name, ohms)

Lookups take roughly constant time thanks to hashing. Keys must be immutable (strings, numbers, tuples). Since Python 3.7, dicts keep insertion order.

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