3.10.3 Assigning a Value & Length of A List

Assigning a Value

To assign values to a list, you can either create the list with initial elements or add items to an existing list.

1. When creating the list: You can directly include values, like [1, 2, 3], in most languages.
2. Add to an empty list: You can start with an empty list ([]) and then use methods like append() or push() to add values to it.
3. Assign to specific positions: You can also assign values to specific positions in the list using an index, such as myList[0] = 5.

Javascript:

%%js
// Create a list with values
let myList = [10, 20, 30];
console.log(myList); // [10, 20, 30]

// Assign values to specific positions
let myList = [];
myList[0] = 5;
myList[1] = 15;
console.log(myList); // [5, 15]

// Append values
let myList = [];
myList.push(100);
myList.push(200);
console.log(myList); // [100, 200]

Python:

# Create a list with values
my_list = [10, 20, 30]
print(my_list)  # [10, 20, 30]

# Assign values to specific positions
my_list = [0] * 3
my_list[0] = 5
print(my_list)  # [5, 0, 0]

# Append values
my_list = []
my_list.append(100)
print(my_list)  # [100]

Common Errors When Assigning

1. Index Out of Range: Assigning a value to a non-existent index in the list.
   • Example: my_list[3] = 4 on a list with only three elements.
2. Incorrect Data Type: Assigning a value of an unexpected type.
   • Example: myArray[1] = "text" in a numeric array.
3. Using += Instead of =: Misusing operators can lead to errors, especially with non-iterable types.
   • Example: my_list += 5 on an integer variable.
4. Syntax Errors: Mistakes in syntax can prevent assignment.
   • Example: Missing parentheses or brackets.

Length of a List

To get the length of a list (i.e., the number of elements it contains), you can use:

JavaScript: .length

Python: len()

These methods return the total number of elements in the list.

Javascript:

%%js
let myList = [10, 20, 30];
console.log(myList.length);  // Output: 3

Python:

my_list = [10, 20, 30]
print(len(my_list))  # Output: 3

Popcorn Hack: Assigning Values to a List and Finding Its Length

Create a list of your five favorite foods.

Add two more items to your list using the .push() method.

Find and print the total number of items in the list using .length