List Comprehension in Python 🚀

🔹 What is List Comprehension?

List comprehension is a concise way to create lists in Python. Instead of using a loop to generate a list, you can use a single-line expression that makes the code more readable and efficient.

💡 Basic Syntax:

new_list = [expression for item in iterable if condition]

• expression → The operation to perform on each item.
• item → The variable representing each element in the iterable.
• iterable → The source (list, tuple, range, etc.).
• condition (optional) → A filter that selects specific items.

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🔹 Example 1: Creating a List

💡 Without List Comprehension

squares = []
for x in range(5):
    squares.append(x**2)
print(squares)  # Output: [0, 1, 4, 9, 16]

✅ With List Comprehension

squares = [x**2 for x in range(5)]
print(squares)  # Output: [0, 1, 4, 9, 16]

🎯 Much shorter and cleaner!

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🔹 Example 2: Filtering with a Condition

💡 Without List Comprehension

even_numbers = []
for x in range(10):
    if x % 2 == 0:
        even_numbers.append(x)
print(even_numbers)  # Output: [0, 2, 4, 6, 8]

✅ With List Comprehension

even_numbers = [x for x in range(10) if x % 2 == 0]
print(even_numbers)  # Output: [0, 2, 4, 6, 8]

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🔹 Example 3: Applying Functions in List Comprehension

words = ["hello", "world", "python"]
uppercase_words = [word.upper() for word in words]
print(uppercase_words)  # Output: ['HELLO', 'WORLD', 'PYTHON']

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🔹 Example 4: Nested List Comprehension

💡 Creating a 2D matrix (3×3)

matrix = [[x for x in range(3)] for y in range(3)]
print(matrix)
# Output: [[0, 1, 2], [0, 1, 2], [0, 1, 2]]

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🔹 Example 5: Using if-else in List Comprehension

numbers = [1, 2, 3, 4, 5]
result = ["Even" if x % 2 == 0 else "Odd" for x in numbers]
print(result)  # Output: ['Odd', 'Even', 'Odd', 'Even', 'Odd']

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🔹 Example 6: Flattening a Nested List

nested_list = [[1, 2, 3], [4, 5], [6, 7, 8]]
flattened = [num for sublist in nested_list for num in sublist]
print(flattened)  # Output: [1, 2, 3, 4, 5, 6, 7, 8]

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🔹 Dictionary & Set Comprehensions (Bonus)

1️⃣ Dictionary Comprehension

squares = {x: x**2 for x in range(5)}
print(squares)  # Output: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

2️⃣ Set Comprehension

unique_numbers = {x % 3 for x in range(10)}
print(unique_numbers)  # Output: {0, 1, 2}

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🔹 Summary Table

Use Case	List Comprehension
Create a list	[x for x in iterable]
Filter elements	[x for x in iterable if condition]
Apply function	[func(x) for x in iterable]
If-else condition	[x if condition else y for x in iterable]
Nested lists	[[x for x in range(3)] for y in range(3)]

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🎯 Advantages of List Comprehension

✅ Faster Execution – More efficient than loops.
✅ Concise & Readable – Reduces lines of code.
✅ Memory Efficient – Can use generators to reduce memory usage.

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