🔹 1. What is a Function in Python?

A function is a reusable block of code that performs a specific task.

Instead of writing the same code again and again, you define once, use many times.

Why functions?

• Reduce code repetition

• Improve readability

• Make code modular & testable

• Easier debugging

---

🔹 2. Basic Function (No Parameters)

Syntax

def function_name():
    statements

Example

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

greet()

📌 Output:

Hello, World!

---

📝 Task 1

Create a function welcome() that prints:

Welcome to Python Programming

---

🔹 3. Function with Parameters (Arguments)

Parameters allow us to pass data into a function.

Example

def greet(name):
    print("Hello", name)

greet("Aarav")
greet("Python")

📌 Output:

Hello Aarav
Hello Python

---

📝 Task 2

Write a function square(n) that prints the square of a number.

---

🔹 4. Function with Return Value

Instead of printing, functions can return values.

Example

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

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

📌 Output:

8

👉 return sends data back to the caller.

---

📝 Task 3

Create a function is_even(n) that returns True if number is even, else False.

---

🔹 5. Types of Arguments in Python

Python supports multiple ways to pass arguments:

---

✅ 5.1 Positional Arguments

Order matters.

def student(name, age):
    print(name, age)

student("Ram", 20)

❌ Wrong order:

student(20, "Ram")  # logical error

---

📝 Task 4

Create a function multiply(a, b, c) and call it using positional arguments.

---

✅ 5.2 Keyword Arguments

You specify parameter names → order doesn’t matter.

def student(name, age):
    print(name, age)

student(age=21, name="Sita")

---

📝 Task 5

Call multiply() using keyword arguments.

---

✅ 5.3 Default Arguments

Provide default values.

def greet(name="User"):
    print("Hello", name)

greet()
greet("Aarav")

---

📝 Task 6

Create a function power(base, exp=2) that returns base raised to power.

---

🔹 6. *args (Variable Length Arguments)

Sometimes you don’t know how many arguments will be passed.

👉 *args stores values as a tuple.

---

Example

def total(*args):
    print(args)
    print(sum(args))

total(1, 2, 3)
total(5, 10, 15, 20)

📌 Output:

(1, 2, 3)
6
(5, 10, 15, 20)
50

---

Key Points

• args is just a name (convention)

• * is important

• Access like a tuple

---

📝 Task 7

Write a function average(*numbers) that returns the average.

---

🔹 7. **kwargs (Keyword Variable Length Arguments)

Used when passing named arguments dynamically.

👉 **kwargs stores data as a dictionary.

---

Example

def student_details(**kwargs):
    print(kwargs)

student_details(name="Aarav", age=21, course="CS")

📌 Output:

{'name': 'Aarav', 'age': 21, 'course': 'CS'}

---

Accessing values

def student_details(**kwargs):
    for key, value in kwargs.items():
        print(key, ":", value)

---

📝 Task 8

Create a function profile(**info) that prints all key-value pairs.

---

🔹 8. Combining Arguments (Advanced)

Correct Order

1. Positional
2. *args
3. Default
4. **kwargs

---

Example

def demo(a, b, *args, x=10, **kwargs):
    print(a, b)
    print(args)
    print(x)
    print(kwargs)

demo(1, 2, 3, 4, x=50, name="Ram", age=20)

---

📝 Task 9

Create a function bill(customer, *items, discount=0, **details)
Print customer, items, discount, and details.

---

🔹 9. Functions as Objects (Advanced Concept)

Functions can be:

• Stored in variables

• Passed as arguments

• Returned from functions

---

Example

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

operation = add
print(operation(3, 4))

---

📝 Task 10

Write a function apply(func, a, b) that applies any function to two numbers.

---

🔹 10. Lambda Functions (Short Functions)

One-line anonymous functions.

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

---

With args

add = lambda *args: sum(args)
print(add(1, 2, 3))

---

📝 Task 11

Create a lambda to check if a number is divisible by 5.

---

🔹 11. Real-World Example (Mini Project)

Student Marks Calculator

def calculate_marks(name, *marks, **extra):
    total = sum(marks)
    avg = total / len(marks)

    print("Name:", name)
    print("Total:", total)
    print("Average:", avg)

    if "grade" in extra:
        print("Grade:", extra["grade"])

calculate_marks(
    "Aarav",
    80, 75, 90,
    grade="A",
    remark="Excellent"
)

---

✅ Final Practice Assignment (Exam-Level)

1. Write a function using default arguments

2. Write a function using *only args

3. Write a function using **only kwargs

4. Combine all argument types in one function

5. Explain difference between print and return

6. Write a real-life example of *args and **kwargs

---