Working with Lists in Python

Creating a List in Python

In Python, a list is an ordered collection of items. To create a list, you can follow these steps:

• Use square brackets: Lists are created by enclosing elements in square brackets [ ].
• Separate items with commas: The items inside the list are separated by commas ,.
• Give the list a name: You can assign the list to a variable. For example, fruits could be the name of your list.

Example 1: Creating a simple list of colors:

# Create a list of colors
colors = ["Red", "Green", "Blue"]
print(colors)  # Output: ["Red", "Green", "Blue"]

In this example, we created a list named colors that contains three items: "Red", "Green", and "Blue".

Example 2: Creating a list with different types of data (Mixed Data):

# A list with different types of data
mixed_list = ["Hello", 42, True, 3.14]
print(mixed_list)  # Output: ["Hello", 42, True, 3.14]

Here, we created a list named mixed_list that contains a string ("Hello"), an integer (42), a boolean value (True), and a floating-point number (3.14). Python allows you to store different types of data in a single list!

Accessing List Elements in Python

In Python, a list is an ordered collection of elements, where each element is assigned an index number. The index helps us access specific elements in the list.

Think of a list like a sequence of houses, where each house has a unique number (index). This number starts at 0 for the first item, and each subsequent item gets the next number.

• First item: Index 0 (Not 1!)
• Second item: Index 1
• Last item: Index -1 (Accessing from the end)

In Python, you can access list elements by specifying their index in square brackets []. Remember, the list indexing starts at 0:

Example:

animals = ["Cat", "Dog", "Elephant", "Giraffe"]
print(animals[0])   # Output: Cat (First item at index 0)
print(animals[2])   # Output: Elephant (Third item at index 2)
print(animals[-1])  # Output: Giraffe (Last item using negative indexing)

Here’s what happens in the example:

• animals[0] accesses the first item in the list, "Cat".
• animals[2] accesses the third item, "Elephant".
• animals[-1] accesses the last item in the list, "Giraffe".

# This will cause an error if the list has less than 4 items!
print(animals[4])

Changing Items in a List

Updating a list is like changing a TV channel. You can directly modify an element in the list by specifying its index.

# Original list
pets = ["Goldfish", "Parrot", "Hamster"]
            
# Change index 1 (Parrot → Dog)
pets[1] = "Dog"
print(pets)  # Output: ["Goldfish", "Dog", "Hamster"]

In this example, the element at index 1 (which is "Parrot") is updated to "Dog". The list now looks like this: ["Goldfish", "Dog", "Hamster"].

Adding Items to a List

There are two common ways to add items to a list:

Method 1: append() - Add to the End of the List

colors = ["Red", "Blue"]
colors.append("Green")
print(colors)  # Output: ["Red", "Blue", "Green"]

The append() method adds an item to the end of the list. Here, we add "Green" to the existing list of colors.

Method 2: insert() - Add at a Specific Position

# Insert "Yellow" at index 1
colors.insert(1, "Yellow")
print(colors)  # Output: ["Red", "Yellow", "Blue", "Green"]

The insert() method allows you to add an item at a specific index in the list. Here, we insert "Yellow" at index 1, which shifts the other items accordingly.

Removing Items from a List

Method 1: remove() - Remove by Value

fruits = ["Apple", "Banana", "Mango"]
fruits.remove("Banana")  # Remove Banana
print(fruits)  # Output: ["Apple", "Mango"]

The remove() method removes the first occurrence of the specified item. In this example, "Banana" is removed from the list, leaving ["Apple", "Mango"].

Method 2: pop() - Remove by Position

# Remove and return the last item
last_fruit = fruits.pop()
print(last_fruit)  # Output: Mango
print(fruits)      # Output: ["Apple"]

The pop() method removes the item at the specified index and returns it. If no index is provided, it removes and returns the last item in the list. In this case, "Mango" is removed from the list.

🚀 Practice Time!

Try this exercise step by step:

# Start with this list
groceries = ["Milk", "Bread", "Eggs"]
            
# 1. Add "Butter" to the end
groceries.append("Butter")
            
# 2. Change "Bread" to "Whole Wheat Bread"
groceries[1] = "Whole Wheat Bread"
            
# 3. Remove "Eggs"
groceries.remove("Eggs")
            
print(groceries)  # Final Output: ["Milk", "Whole Wheat Bread", "Butter"]

This exercise helps you practice adding, changing, and removing items from a list step by step.

❓ Common Questions

Q: Can a list have duplicate values?
A: Yes! A list can contain the same value multiple times. For example, [1, 1, 2] is a valid list.

Q: How to check the length of a list?
A: You can use the built-in len() function to check the length of a list (i.e., how many items are in it). For example: print(len(fruits))