🧩 Python Lambda Functions Guide

Beginner-friendly documentation about Python lambda functions, anonymous functions, and common functional programming patterns.

This document explains: - what lambda functions are - lambda syntax - common use cases - map() - filter() - sorted() - practical examples - common mistakes

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📚 Table of Contents

• 📖 What is a Lambda Function?
• 🧱 Basic Syntax
• ⚙️ Lambda vs Normal Functions
• 📦 Returning Values
• 🔗 Using Multiple Arguments
• 🗂️ Lambda with sorted()
• 🧪 Lambda with map()
• 🔍 Lambda with filter()
• 🎮 Real 42 Examples
• ⚠️ Common Beginner Mistakes
• 📚 Best Practices
• 📚 Final Notes

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📖 What is a Lambda Function?

A lambda function is: - a small anonymous function - created in a single line - often used for quick operations

Unlike normal functions: - lambda functions usually do not have names

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🧱 Basic Syntax

lambda arguments: expression

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Simple Example

square = lambda x: x * x

print(square(5))

Output:

25

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Equivalent Normal Function

def square(x):
    return x * x

Both functions behave the same way.

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⚙️ Lambda vs Normal Functions

Lambda Function

lambda x: x + 1

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Normal Function

def add_one(x):
    return x + 1

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📦 Returning Values

Lambda functions automatically return the expression result.

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🔗 Using Multiple Arguments

add = lambda a, b, c: a + b + c

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🗂️ Lambda with sorted()

players.sort(key=lambda player: player[1])

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🧪 Lambda with map()

numbers = [1, 2, 3]

result = list(map(lambda x: x * 2, numbers))

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🔍 Lambda with filter()

numbers = [1, 2, 3, 4]

evens = list(filter(lambda x: x % 2 == 0, numbers))

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🎮 Real 42 Examples

Sorting Coordinates

positions.sort(key=lambda pos: pos[0])

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Filtering Valid Zones

valid_zones = list(filter(lambda zone: zone.active, zones))

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⚠️ Common Beginner Mistakes

❌ Trying to Use Multiple Lines

Wrong:

lambda x:
    x + 1

Lambda functions must stay on ONE line.

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❌ Forgetting list()

map() and filter() return iterators.

Usually convert them:

list(map(...))

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📚 Best Practices

• Use lambdas for short operations
• Prefer normal functions for complex logic
• Keep lambdas readable
• Avoid nested lambdas

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📚 Final Notes

Lambda functions are extremely common in modern Python.

They are especially useful for: - quick transformations - sorting - filtering - concise operations

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