Lambda Functions in Python

Lambda functions are small, one-line functions that do not require a name. They are useful when you want to create quick, simple functions without writing a full def block. Python developers commonly use lambda functions for data processing, filtering, mapping, and sorting.

What Is a Lambda Function?

A lambda function is an anonymous (nameless) function. It contains only one expression and automatically returns the result of that expression.

lambda arguments : expression

This means:
• Write lambda
• Provide the inputs
• Write a single expression that produces a result

Example 1: Basic Lambda Function

This lambda function doubles a number:

double = lambda x: x * 2
print(double(5))

Output: 10

Example 2: Lambda With Multiple Inputs

add = lambda a, b: a + b
print(add(10, 20))

Output: 30

When Should You Use Lambda?

Lambda functions are helpful when:

• You need a short, temporary function
• You want cleaner, shorter code
• You are working with map(), filter(), or sorted()
• You need to pass a function as an argument

Using Lambda With map()

The map() function applies the lambda to every element of a list.

numbers = [1, 2, 3, 4, 5]
squares = list(map(lambda x: x * x, numbers))
print(squares)

Output: [1, 4, 9, 16, 25]

Using Lambda With filter()

filter() keeps only the elements that satisfy the condition.

numbers = [10, 15, 20, 25, 30]
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(evens)

Output: [10, 20, 30]

Using Lambda With sorted()

Lambda helps Python decide how sorting should happen.

students = [
    ("Rahul", 85),
    ("Anjali", 92),
    ("Kiran", 78)
]

sorted_list = sorted(students, key=lambda x: x[1])
print(sorted_list)

Output: [('Kiran', 78), ('Rahul', 85), ('Anjali', 92)]

Lambda vs Normal Function

Real-World Example: Discount Calculator

discount_price = lambda price, discount: price - (price * discount / 100)

print(discount_price(1000, 10))

Output: 900

📝 Practice Exercises

Exercise 1

Create a lambda function that adds 5 to a number.

Exercise 2

Use lambda + map() to convert a list of names to uppercase. Example list: ["sree", "kiran", "aarav"]

Exercise 3

Use lambda + filter() to return numbers greater than 50 from: [10, 55, 43, 90, 12, 75]

Exercise 4

Use lambda + sorted() to sort this list based on age: ("Ravi", 21), ("Karthik", 18), ("Meena", 25)

✅ Practice Answers

Answer 1

add_five = lambda x: x + 5
print(add_five(10))

Answer 2

names = ["sree", "kiran", "aarav"]
upper_names = list(map(lambda n: n.upper(), names))
print(upper_names)

Answer 3

numbers = [10, 55, 43, 90, 12, 75]
result = list(filter(lambda x: x > 50, numbers))
print(result)

Answer 4

people = [("Ravi", 21), ("Karthik", 18), ("Meena", 25)]
sorted_people = sorted(people, key=lambda x: x[1])
print(sorted_people)