Home / Python / Day 4: Functions & Modules / Lambda Functions

Lambda Functions

Lambda functions are small anonymous functions written in a single line.

Lambda Functions

A lambda is a small anonymous function. It can take any number of arguments but can only have one expression.

Syntax: lambda args: expression

Syntax

<pre><code># Basic lambda
add = lambda x, y: x + y
print(add(3, 5))  # 8

# Lambda with sorted()
people = [("Alice", 25), ("Bob", 20), ("Charlie", 30)]
people.sort(key=lambda person: person[1])  # Sort by age
print(people)

# Lambda with map()
numbers = [1, 2, 3, 4, 5]
squares = list(map(lambda x: x**2, numbers))
print(squares)  # [1, 4, 9, 16, 25]

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

# When to use lambda vs def
# Lambda: simple, one-line, used inline
# def: complex, multi-line, reusable with name
</code></pre>

Revision Notes

• lambda args: expression — anonymous function
• Single expression only (no statements)
• Often used with sorted(), map(), filter()
• Prefer def for anything complex
• key=lambda in sorting is the main use case

Apply Discount with Lambda

Easy

Write a function apply_discount(prices, percent) that takes a list of prices and a discount percentage, and returns a new list with each price reduced by that percentage. Use a lambda function with map().

Input:

prices=[100, 200, 50], percent=10

Output:

[90.0, 180.0, 45.0]

Show Hint

discount_factor = 1 - percent/100. Use map(lambda p: round(p * discount_factor, 2), prices).

Solve this Challenge

Show Solution

def apply_discount(prices, percent):
    factor = 1 - percent / 100
    return list(map(lambda p: round(p * factor, 2), prices))

print(apply_discount([100, 200, 50], 10))

Functions Modules & Packages

Lambda Functions