A lambda function in Python is an anonymous, inline function used for simple operations. It's ideal for short functions that are used only once or temporarily.

 What is a Lambda Function?

• It has no name (anonymous).
• Defined using the lambda keyword.
• Can have any number of arguments, but only one expression.
• The result of the expression is automatically returned.

Syntax

lambda arguments: expression

Equivalent to:

def function(arguments):
   return expression

Example 1: Basic Lambda Function

square = lambda x: x * x
print(square(5))

Output:

25

Example 2: Lambda with Multiple Arguments

add = lambda a, b: a + b
print(add(3, 7))

Output:

10

Example 3: Lambda with No Arguments

say_hello = lambda: "Hello!"
print(say_hello())

Output:

Hello!

Example 4: Using Lambda in sorted()

Sort list of tuples by second element:

pairs = [(1, 2), (3, 1), (5, 0)]
sorted_pairs = sorted(pairs, key=lambda x: x[1])
print(sorted_pairs)

Output:

[(5, 0), (3, 1), (1, 2)]

Example 5: Using Lambda with map()

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

Output:

[1, 4, 9, 16]

Example 6: Using Lambda with filter()

nums = [1, 2, 3, 4, 5, 6]
even = list(filter(lambda x: x % 2 == 0, nums))
print(even)

Output:

[2, 4, 6]

Example 7: Using Lambda with reduce()

from functools import reduce
product = reduce(lambda x, y: x * y, [1, 2, 3, 4])
print(product)

Output:

24

Lambda vs def

When Not to Use Lambda

• Avoid lambdas for complex logic.
• Don't use them if code readability matters more.

Practice Task

Convert this function into a lambda:

def double(x):
   return x * 2
# Lambda version
double = lambda x: x * 2
print(double(10))  # Output: 20

Summary

• Use lambda for quick, small, one-line functions.
• Commonly used with functions like map(), filter(), sorted(), and reduce().
• Avoid using it for complex logic — use def instead.