8.5 Dictionaries

Notes

A dictionary stores key: value pairs inside curly braces. You look up a value by its key.

ages = {"Ana": 15, "Ben": 16}
print(ages["Ana"])
ages["Cy"] = 14
print(len(ages))

• This prints 15, then 3 after adding a new key.
• key in ages checks for a key. ages.get("Zed", 0) returns 0 if the key is missing instead of an error.
• Looking up a missing key with square brackets causes a KeyError.
• Keys must be unique. Use for key in ages: to loop through the keys.
• Use a dictionary when you look up by a name or label; use a list when order and position matter.