Lists and Arrays, Ordered Sequences

So far each variable has held a single value. But programs work with many things: every student in a class, every book on a shelf, every transaction in a day.

A Python list and a JavaScript array are the same idea: an ordered sequence of values in one container. They're a direct equivalent, one of the cleanest translations between the two languages.

Creating a sequence

PYTHON

cities = ["Accra", "Atlanta", "Kingston"]

JAVASCRIPT

let cities = ["Accra", "Atlanta", "Kingston"];

Compare → Square brackets, comma-separated values: identical syntax. Python calls it a list; JavaScript calls it an array. The name differs; the concept and the notation do not.

EXAMPLE

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YOUR TURN

Your turn → Index 0 is the first item, always. Add a fourth city and print it by its index.

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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.

✦ Zero-indexing, one more time

Position 0 is first, position 1 is second. A list of 3 items has valid indexes 0, 1, and 2. Asking for index 3 is asking for a fourth item that doesn't exist, Python raises an IndexError, JavaScript quietly returns undefined.

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