Python Functions: Defining Functions 🎯

A function in Python is a reusable block of code that performs a specific task. Functions help reduce redundancy, increase readability, and make code modular.

1️⃣ Defining a Function (Using def Keyword)

🔹 Basic Function Syntax

def function_name():
# Function body (indented)
print("Hello, World!")

# Calling the function
function_name()
# Output: Hello, World!

🔹 Function with Parameters

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

greet("Alice") # Output: Hello, Alice!
greet("Bob") # Output: Hello, Bob!

🔹 Function with Return Value


def square(number):
return number * number

result = square(5)
print(result) # Output: 25

2️⃣ Function Arguments & Parameters

Python functions can have different types of arguments:

Argument Type Example
Positional Arguments greet("Alice")
Default Arguments greet(name="Guest")
Keyword Arguments greet(name="Bob")
Arbitrary Arguments (*args) sum_all(1, 2, 3, 4)
Arbitrary Keyword Arguments (**kwargs) person_info(name="Alice", age=25)

🔹 Positional & Default Arguments


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

greet() # Output: Hello, Guest!
greet("Alice") # Output: Hello, Alice!

🔹 Keyword Arguments

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

person_info(age=25, name="Bob")
# Output: Name: Bob, Age: 25
🔹 Arbitrary Arguments (*args)
Used when we don’t know how many arguments will be passed.


def sum_all(*numbers):
return sum(numbers)

print(sum_all(1, 2, 3, 4, 5)) # Output: 15

🔹 Arbitrary Keyword Arguments (**kwargs)
Used when we don’t know how many keyword arguments will be passed.


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

display_info(name="Alice", age=25, city="New York")

# Output:
# name: Alice
# age: 25
# city: New York

3️⃣ Return Statement & Multiple Returns

🔹 Returning a Value

def multiply(x, y):
return x * y

result = multiply(4, 5)
print(result) # Output: 20

🔹 Returning Multiple Values

def get_coordinates():
return 10, 20 # Returns a tuple

x, y = get_coordinates()
print(x, y) # Output: 10 20

4️⃣ Nested Functions & Scope

🔹 Nested Functions

def outer_function():
print("Outer function")

def inner_function():
print("Inner function")

inner_function()

outer_function()
# Output:
# Outer function
# Inner function

🔹 Variable Scope (Local & Global)

global_var = "I am global"

def my_function():
local_var = "I am local"
print(global_var) # ✅ Can access global variable
print(local_var) # ✅ Can access local variable

my_function()

# print(local_var) # ❌ Error: local_var is not accessible outside the function

5️⃣ Lambda (Anonymous) Functions

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


square = lambda x: x * x
print(square(4)) # Output: 16

6️⃣ When to Use Functions?

✅ When you need code reusability.

✅ When you want better readability.

✅ When you need modularity in your program.

    Date: 2025-03-22 00:00:00.000000