Coding Concept - Lists

3.10 Lists - Syntax Terrors

JavaScript Lists Homework Python Lists Homework

Creating Lists

Key Points

Define lists with []
Store multiple values
Mix data types

JavaScript


let colors = ["red", "green", "blue"];
console.log(colors);

In JavaScript, you create a list (array) using [].

let colors = ["red", "green", "blue"]; creates an array called colors with three items.
Arrays can hold numbers, strings, or other arrays.
console.log(colors); prints the array to the console.

Arrays are a flexible way to store groups of values in JavaScript.

Python


colors = ["red", "green", "blue"]
print(colors)

In Python, you create a list using [].

colors = ["red", "green", "blue"] creates a list called colors with three items.
Lists can hold numbers, strings, or other lists.
print(colors) displays the list.

Lists are a basic way to store and organize data in Python.

Accessing Elements

Key Points

Use indexes to access items
Start counting at 0
Access first, last, or middle elements

JavaScript


let animals = ["cat", "dog", "bird"];
console.log(animals[1]); // dog
console.log(animals[animals.length - 1]); // bird

JavaScript arrays are zero-indexed, meaning the first item is at position 0.

animals[1] gets the second item ("dog").
animals[animals.length - 1] gets the last item ("bird").

Use indexes to access any element in the array.

Python


animals = ["cat", "dog", "bird"]
print(animals[1])  # dog
print(animals[-1]) # bird

Python lists are zero-indexed, so the first item is at position 0.

animals[1] gets the second item ("dog").
animals[-1] gets the last item ("bird").

Use indexes to access any element in the list.

Modifying Lists

Key Points

Change values by index
Update existing items
Keep lists dynamic

JavaScript


let scores = [10, 20, 30];
scores[0] = 15;
scores[2] = scores[0] + scores[1];
console.log(scores); // [15, 20, 35]

You can change an array item by assigning a new value to its index.

scores[0] = 15; replaces 10 with 15.
scores[2] = scores[0] + scores[1]; updates the last item to the sum of the first two.

Arrays are dynamic and can be changed anytime.

Python


scores = [10, 20, 30]
scores[0] = 15
scores[2] = scores[0] + scores[1]
print(scores)  # [15, 20, 35]

You can change a list item by assigning a new value to its index.

scores[0] = 15 replaces 10 with 15.
scores[2] = scores[0] + scores[1] updates the last item to the sum of the first two.

Lists are dynamic and can be changed anytime.

Adding Elements

Key Points

Use append/push to add to the end
Insert at specific positions
Grow lists dynamically

JavaScript


let cities = ["Paris", "London"];
cities.push("Tokyo");
cities.splice(1, 0, "Berlin");
console.log(cities); // ["Paris", "Berlin", "London", "Tokyo"]

push() adds an item to the end of the array.
splice() can insert items at any position.
console.log(cities); prints the final array.

Arrays can grow as you add more items.

Python


cities = ["Paris", "London"]
cities.append("Tokyo")
cities.insert(1, "Berlin")
print(cities)  # ["Paris", "Berlin", "London", "Tokyo"]

append() adds an item to the end of the list.
insert() can add items at any position.
print(cities) prints the final list.

Lists can grow as you add more items.

Removing Elements

Key Points

Remove by value
Remove by index
Pop the last element

JavaScript


let colors = ["red", "green", "blue", "yellow"];
colors.splice(2, 1); // Remove item at index 2 ("blue")
colors.pop(); // Remove last item ("yellow")
console.log(colors); // ["red", "green"]

splice() removes items by index.
pop() removes the last item.
console.log(colors); prints the updated array.

You can remove items from arrays by value or index.

Python


colors = ["red", "green", "blue", "yellow"]
colors.remove("blue")
colors.pop()
print(colors)  # ["red", "green"]

remove() removes an item by value.
pop() removes the last item.
print(colors) prints the updated list.

You can remove items from lists by value or index.

Looping Through Lists

Key Points

Use for loops to iterate
Process each element
Use for…of in JavaScript

JavaScript


let animals = ["cat", "dog", "bird"];
// Complete traversal
for (let animal of animals) {
    console.log(animal);
}
// Partial traversal
for (let i = 0; i < 2; i++) {
    console.log(animals[i]);
}

for...of loops go through each item in the array.
Use a regular for loop for partial traversal.

Looping lets you process every element in an array.

Python


animals = ["cat", "dog", "bird"]
# Complete traversal
for animal in animals:
    print(animal)
# Partial traversal
for i in range(0, 2):
    print(animals[i])

for loops go through each item in the list.
Use range() for partial traversal.

Looping lets you process every element in a list.