⚡ List and Dictionary Comprehension in Python | Lesson 11

⚡ List and Dictionary Comprehension in Python

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List and dictionary comprehensions are powerful, compact ways to create and transform lists or dictionaries in a single line of code. They help you write cleaner, faster, and more readable code compared to traditional loops! Let’s explore how to use them with examples and a fun small project. 🚀

1. List Comprehension 📝

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A concise way to create or transform a list.

Syntax:

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[expression for item in iterable if condition]

• expression is what you want to include in the new list.
• iterable is a sequence or collection you loop over.
• Optional if condition filters items.

Example:

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Create a list of squares for numbers 1 to 5.

squares = [x**2 for x in range(1, 6)]
print(squares)  # [1, 4, 9, 16, 25]

Filter to include only even squares:

even_squares = [x**2 for x in range(1, 6) if x % 2 == 0]
print(even_squares)  # [4, 16]

2. Dictionary Comprehension 📚

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Create a dictionary from an iterable, also compact and clear.

Syntax:

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{key_expression: value_expression for item in iterable if condition}

Example:

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Create a dictionary where keys are numbers 1 to 5 and values are their cubes.

cubes = {x: x**3 for x in range(1, 6)}
print(cubes)  
# {1: 1, 2: 8, 3: 27, 4: 64, 5: 125}

Filter to include only numbers where cube is > 20:

filtered_cubes = {x: x**3 for x in range(1, 6) if x**3 > 20}
print(filtered_cubes)  
# {3: 27, 4: 64, 5: 125}

Small Project: Create a Student Grade Dictionary 🎓

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Goal: Given a list of student names and their scores, create a dictionary that stores each student’s name as the key and their grade (Pass/Fail) as the value based on if the score is ≥ 50.

Step 1: Define the data

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students = ["Riya", "Aman", "Nina", "Sam"]
scores = [65, 45, 75, 30]

Step 2: Use dictionary comprehension with condition

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grade_dict = {students[i]: ("Pass" if scores[i] >= 50 else "Fail") for i in range(len(students))}
print(grade_dict)

Output:

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{'Riya': 'Pass', 'Aman': 'Fail', 'Nina': 'Pass', 'Sam': 'Fail'}

Practice Questions 🏆

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1. Use list comprehension to create a list of even numbers between 1 and 20.
2. Use dictionary comprehension to create a dictionary of numbers (1 to 10) and their squares.
3. Modify the student project to add a “Distinction” grade for scores ≥ 75.

Checklist for This Chapter ✅

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• Used list comprehension for creating lists
• Used dictionary comprehension to build dictionaries
• Applied conditions inside comprehensions
• Built a practical small project application

You’re now ready to write elegant, efficient code with comprehensions! Keep experimenting and watch your programs get cleaner and faster! ✨