Learn Python in 30 Days - Day 7: Lists in Python

 Learn Python in 30 Days - Day 7: Lists in Python

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Welcome to Day 7! Today, we’ll dive into lists, one of the most versatile and commonly used data structures in Python. Lists allow you to store and manipulate multiple items in a single variable. Let’s explore how to use them effectively!

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1. What is a List?

A list is an ordered collection of items (of any data type) in Python. Lists are:

• Mutable (you can change them).
• Indexed (you can access elements by their position).
• Versatile (can store different data types in the same list).

Example:

my_list = ["apple", "banana", "cherry"]

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2. Creating Lists

Example:

# A list of strings
names = ["Farjana Akter Mim", "Rahim", "Karim"]

# A list of integers
ages = [21, 25, 30]

# A mixed list
mixed = ["Brahmanbaria", 21, True]

# An empty list
empty = []

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3. Accessing Elements

Use indexing to access elements in a list. Indexing starts at 0.

Example:

names = ["Farjana Akter Mim", "Rahim", "Karim"]

# First element
print(names[0])  # Output: Farjana Akter Mim

# Last element
print(names[-1])  # Output: Karim

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4. Modifying Lists

You can update, add, or remove elements from a list.

Updating Elements:

names = ["Farjana Akter Mim", "Rahim", "Karim"]
names[1] = "Abdul"
print(names)  # Output: ['Farjana Akter Mim', 'Abdul', 'Karim']

Adding Elements:

• Using append(): Adds an element to the end of the list.
• Using insert(): Adds an element at a specific position.

names = ["Farjana Akter Mim", "Rahim"]
names.append("Karim")
print(names)  # Output: ['Farjana Akter Mim', 'Rahim', 'Karim']

names.insert(1, "Nusrat")
print(names)  # Output: ['Farjana Akter Mim', 'Nusrat', 'Rahim', 'Karim']

Removing Elements:

• Using remove(): Removes a specific value.
• Using pop(): Removes an element by index and returns it.
• Using del: Deletes an element or the entire list.

names = ["Farjana Akter Mim", "Rahim", "Karim"]
names.remove("Rahim")
print(names)  # Output: ['Farjana Akter Mim', 'Karim']

removed = names.pop(0)
print(removed)  # Output: Farjana Akter Mim
print(names)  # Output: ['Karim']

del names[0]
print(names)  # Output: []

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5. Iterating Over Lists

Use a for loop to iterate over a list.

Example:

names = ["Farjana Akter Mim", "Rahim", "Karim"]

for name in names:
    print(name)

Output:

Farjana Akter Mim
Rahim
Karim

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6. Common List Operations

Operation	Code Example	Output
Length of a list	len(names)	3
Check if item exists	"Rahim" in names	True
Sorting a list	names.sort()	Sorted list alphabetically
Reverse a list	names.reverse()	List in reverse order
Copy a list	new_list = names.copy()	A new copy of the list

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7. Slicing Lists

You can extract a portion of a list using slicing.

Syntax:

list[start:end]  # Elements from 'start' to 'end-1'

Example:

names = ["Farjana Akter Mim", "Rahim", "Karim", "Nusrat", "Habib"]

# Get first three elements
print(names[0:3])  # Output: ['Farjana Akter Mim', 'Rahim', 'Karim']

# Get elements from index 2 to the end
print(names[2:])  # Output: ['Karim', 'Nusrat', 'Habib']

# Get every second element
print(names[::2])  # Output: ['Farjana Akter Mim', 'Karim', 'Habib']

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8. Nested Lists

Lists can contain other lists.

Example:

data = [
    ["Farjana Akter Mim", 21, "Brahmanbaria"],
    ["Rahim", 25, "Dhaka"],
    ["Karim", 30, "Chattogram"]
]

# Accessing Nested Elements
print(data[0][0])  # Output: Farjana Akter Mim
print(data[2][2])  # Output: Chattogram

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9. Practice Tasks for Day 7

Task 1: Create a List of Your Favorite Movies

Write a program to create and print a list of your top 5 favorite movies.

Task 2: Find the Largest Number in a List

numbers = [5, 12, 8, 21, 7]
print("Largest number:", max(numbers))

Task 3: Reverse a List

Write a program to reverse the order of items in a list without using the reverse() method.

Task 4: Check for Palindromes

Write a program to check if a list of strings contains any palindromes.

Example:

words = ["radar", "python", "level", "world"]
for word in words:
    if word == word[::-1]:
        print(f"'{word}' is a palindrome.")

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10. Common Mistakes to Avoid

1. Index Out of Range:
   Ensure you don’t access indexes beyond the size of the list.

   names = ["Farjana Akter Mim", "Rahim"]
   print(names[2])  # Error: Index out of range
   

2. Mutating the List While Iterating:
   Modifying a list while iterating can lead to unexpected behavior.

3. Copying by Reference Instead of Value:
   Use .copy() to create a separate copy of a list.

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11. Pro Tips for Day 7

• Use list comprehensions for concise and efficient operations.
• Explore built-in functions like sum(), min(), and max() for numerical lists.
• Practice combining lists with loops for real-world tasks.

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🎯 Day 7 Goal:
Practice creating, modifying, and slicing lists. Write at least 5 programs using lists for different operations.

Let me know when you’re ready for Day 8! 🚀