Dictionaries and Objects, Labeled Data

Lists work when position carries meaning. But most real data has labels: a person has a name, an age, a city, not an item 0, item 1, item 2.

A Python dictionary and a JavaScript object both store key → value pairs. You look things up by name instead of position.

Labeled records

PYTHON

elder = {
    "name": "Fannie Lou Hamer",
    "born": 1917,
    "state": "Mississippi"
}
print(elder["name"])

JAVASCRIPT

let elder = {
  name: "Fannie Lou Hamer",
  born: 1917,
  state: "Mississippi"
};
console.log(elder.name);

Compare → Curly braces and key: value pairs in both. Two real differences: Python REQUIRES quotes around keys; JavaScript usually omits them. And Python accesses with square brackets, elder["name"], while JavaScript prefers dot notation, elder.name (though elder["name"] also works).

EXAMPLE

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YOUR TURN

Your turn → Assigning to a key that doesn't exist CREATES it. Add a field for a notable quote, then print the whole record.

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Syntax has to be exact. Every quote, bracket and parenthesis needs its partner, and in Python the spaces at the start of a line count. One slip and the program won't run; the message will say where.

Now the pattern that makes real applications possible: a list of dictionaries (Python) or an array of objects (JavaScript). This is how nearly every dataset on earth is shaped, every API response, every database query result, every spreadsheet.

EXAMPLE

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YOUR TURN

Your turn → Read it in two steps: users[1] gets the second record, then.name reaches inside it. Add a third user and print their age.

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Syntax has to be exact. Every quote, bracket and parenthesis needs its partner, and in Python the spaces at the start of a line count. One slip and the program won't run; the message will say where.

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