Functions and Lambda Expressions

1. Introduction

Functions allow code reuse by defining blocks that can be executed multiple times. Python also supports lambda expressions, which provide a quick way to define simple functions.

2. Defining Functions in Python

A function is defined using the def keyword.

Syntax

def function_name(parameters):
    # Function body
    return value  # Optional

Example: Simple Function

def greet():
    print("Hello, World!")

greet()

Output

Hello, World!

3. Function Parameters and Arguments

Example: Function with Parameters

def greet(name):
    print(f"Hello, {name}!")

greet("Aayush")

Output

Hello, Aayush!

Multiple Parameters

def add(a, b):
    return a + b

result = add(5, 3)
print(result)

Output

8

4. Default Arguments

Default values can be assigned to function parameters.

def power(base, exponent=2):
    return base ** exponent

print(power(3))      # Uses default exponent (2)
print(power(3, 3))   # Uses provided exponent (3)

Output

9
27

5. Keyword Arguments (kwargs)

Allows passing arguments using key-value pairs.

def person_info(name, age):
    print(f"Name: {name}, Age: {age}")

person_info(age=25, name="Ankit")  # Order does not matter

Output

Name: Ankit, Age: 25

Arbitrary Keyword Arguments (**kwargs)

Allows passing multiple named arguments.

def print_info(**info):
    for key, value in info.items():
        print(f"{key}: {value}")

print_info(name="Ankit", age=30, city="Delhi")

Output

name: Ankit
age: 30
city: Delhi

6. Returning Values from Functions

A function can return a value using return.

def multiply(a, b):
    return a * b

result = multiply(4, 5)
print(result)

Output

20

7. Lambda Functions (Anonymous Functions)

A lambda function is a one-line function without a name.

Syntax

lambda arguments: expression

Example: Lambda Function

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

Output

25

Using Lambda in map()

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

Output

[1, 4, 9, 16]

Using Lambda in filter()

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

Output

[2, 4, 6]

8. Nested Functions

A function inside another function.

def outer():
    def inner():
        print("Inside inner function")
    inner()

outer()

Output

Inside inner function

9. Function Scope (Local vs. Global Variables)

• Local variables exist only inside a function.
• Global variables exist outside functions and can be accessed within functions.

Example

x = 10  # Global variable

def show():
    x = 5  # Local variable
    print("Inside function:", x)

show()
print("Outside function:", x)

Output

Inside function: 5
Outside function: 10

10. Summary

Functions allow code reuse and modularity.
Functions can have parameters, return values, and default arguments.
Lambda expressions provide a compact way to define functions.
map() and filter() work well with lambda functions.
**kwargs allows handling multiple keyword arguments.