? Python Lambda Functions

⚡ Quick Overview

A lambda function in Python is a small anonymous function defined using the lambda keyword. It can have any number of arguments but only one expression, and that expression is automatically returned.

Used for short, throwaway functions.
Common with map(), filter(), and sorted().
Perfect when you need a function as an argument in just one place.

? Key Concepts

Anonymous: Lambda functions usually have no name (unlike functions defined with def).
Single expression: They contain exactly one expression, whose result is returned.
Any number of arguments: You can pass multiple inputs, but still only one expression.
Inline usage: Designed to be used where they are defined, often as arguments.
Readability trade-off: Great for short logic, but longer lambdas hurt readability.

? Syntax and Theory

The basic syntax of a lambda function is:

? View Lambda Syntax

lambda arguments: expression
# Basic lambda function syntax

This creates an anonymous function object. For example, lambda x: x * 2 represents a function that doubles its argument.

You can assign a lambda to a variable (giving it a name), or pass it directly into higher-order functions like map(), filter(), and sorted().

? Code Examples

Lambda functions can be used wherever functions are required.

➕ Lambda to add two numbers

# Example 1: Lambda to add two numbers
add = lambda a, b: a + b
print(add(5, 3))  # 8

? Lambda with map() to square numbers

# Example 2: Lambda with map
numbers = [1, 2, 3, 4]
squared = list(map(lambda x: x**2, numbers))
print(squared)  # [1, 4, 9, 16]

? Lambda with filter() to get even numbers

# Example 3: Lambda with filter
numbers = [1, 2, 3, 4]
even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
print(even_numbers)  # [2, 4]

? Output and Explanation

▶️ What this code does

add(5, 3) uses a lambda to add two numbers and prints 8.
map(lambda x: x**2, numbers) applies the lambda to every element in [1, 2, 3, 4], producing [1, 4, 9, 16].
filter(lambda x: x % 2 == 0, numbers) keeps only numbers divisible by 2, giving [2, 4].

In all these cases, the lambda replaces a separately defined function. This keeps the code short and focused when the logic is simple.

? Use Cases

Short, throwaway functions without defining a named function.
Using with functions like map(), filter(), and sorted().
When a small function is needed as an argument in only one place.
Custom sorting keys, such as sorting a list of tuples by a specific element.

? Tips & Best Practices

Use lambda functions for concise, simple operations.
Prefer regular def functions if the logic is complex or reused.
Remember that lambda functions can only have one expression (no multiple statements).
Keep lambdas short so your code remains readable for others (and your future self!).

? Try It Yourself

Create a lambda function to multiply two numbers.
Use lambda with map() to cube a list of numbers.
Use lambda with filter() to extract odd numbers from a list.
Use lambda in sorted() to sort a list of tuples by the second element.
Rewrite a small existing def function as a lambda (if the logic is simple enough).