List, Set and Dictionary Comprehension

What is List Comprehension?

List Comprehension means list comprehension creates a new list in a compact and readable way using an expression and a loop.

In real programs, this topic helps in filtering lists quickly. Learn the idea first, then type the program yourself and compare the output.

Why should you learn this?

• It is useful for filtering lists quickly.
• It connects with transforming data in one line.
• It improves your ability to read, write and debug Python programs.

Important Terms

These terms are used directly in this lesson. Understand them before memorising the code.

Syntax / Basic Pattern

The simple pattern is: prepare data, apply the concept, then show the result.

numbers = [1, 2, 3, 4, 5, 6]
squares = [n * n for n in numbers]
even_squares = [n * n for n in numbers if n % 2 == 0]
print(squares)
print(even_squares)

Complete Example Program

numbers = [1, 2, 3, 4, 5, 6]

squares = [n * n for n in numbers]
even_squares = [n * n for n in numbers if n % 2 == 0]

print(squares)
print(even_squares)

Expected Output

Program Explanation

• numbers = [1, 2, 3, 4, 5, 6] stores a value in numbers.
• squares = [n * n for n in numbers] stores a value in squares.
• even_squares = [n * n for n in numbers if n % 2 == 0] performs the next step of the program logic.
• print(squares) displays information or calculated result on the screen.
• print(even_squares) displays information or calculated result on the screen.

Where will you use it?

• Filtering lists quickly.
• Transforming data in one line.
• Writing concise readable code.

Common Mistakes

• Making code complex when a simple function or class is enough.
• Not handling possible errors or edge cases.
• Mixing project dependencies instead of using a virtual environment.

Practice Tasks

1. Type the program in list-comprehension.py and run it.
2. Change input values or sample data and observe the new output.
3. Create one example related to filtering lists quickly.
4. Write 5 lines explaining the logic in your own words.

Summary

List Comprehension is not a theory-only topic. You should be able to explain the meaning, write the example, run it successfully, and use it in a small practical program.