📘 Lesson 7: Functions in Python examples

🔹 1. What is a Function?

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

👉 Instead of writing the same code again and again, we define it once and reuse it.

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🔹 2. Why Use Functions?

✔ Avoid repetition
✔ Make code reusable
✔ Improve readability
✔ Easy debugging

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🔹 3. Defining a Function

Syntax

def function_name():
    # code block

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Example 1: Simple Function

def greet():
    print("Hello, welcome to Python")

🔹 Calling the function:

greet()

Output

Hello, welcome to Python

📌 Explanation

• def keyword defines a function
• greet is the function name
• Function runs only when called

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🔹 4. Function with Parameters

Parameters allow us to pass data into a function.

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Example 2: Greeting with Name

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

🔹 Calling the function:

greet("Sameer")
greet("Ayesha")

Output

Hello Sameer
Hello Ayesha

📌 Explanation

• name is a parameter
• Values passed are called arguments

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🔹 5. Function with Multiple Parameters

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Example 3: Student Details

def student_info(name, age):
    print("Name:", name)
    print("Age:", age)

🔹 Function call:

student_info("Saddam", 24)

Output

Name: Saddam
Age: 24

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🔹 6. Function with Return Value

Functions can return a value using return.

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Example 4: Add Two Numbers

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

🔹 Function call:

result = add(10, 5)
print(result)

Output

15

📌 Explanation

• return sends value back to caller
• Code after return does not execute

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🔹 7. Return vs Print

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Example 5

def show_sum(a, b):
    print(a + b)

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

show_sum(5, 5)
print(get_sum(5, 5))

Output

10
10

📌 Explanation

• print() → displays value
• return → gives value for further use

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🔹 8. Function with User Input

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Example 6

def square_number():
    num = int(input("Enter a number: "))
    print("Square:", num * num)

🔹 Function call:

square_number()

Sample Output

Enter a number: 4
Square: 16

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🔹 9. Default Parameter Value

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Example 7

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

greet()
greet("Chandini")

Output

Hello Guest
Hello Chandini

📌 Explanation

• Default value is used if argument not provided

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🔹 10. Keyword Arguments

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Example 8

def employee(name, salary):
    print("Name:", name)
    print("Salary:", salary)

employee(salary=30000, name="Gousya")

Output

Name: Gousya
Salary: 30000

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🔹 11. Function Calling Another Function

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Example 9

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

def calculate():
    result = add(3, 4)
    print("Result:", result)

calculate()

Output

Result: 7

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🔹 12. Real-Life Example: Salary Calculator

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Example 10

def total_salary(basic, bonus):
    return basic + bonus

salary = total_salary(25000, 5000)
print("Total Salary:", salary)

Output

Total Salary: 30000

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🔹 13. Common Mistakes (IMPORTANT)

❌ Forgetting to call function
❌ Wrong indentation
❌ Missing return value
❌ Confusing print with return

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🧠 Final Summary

✔ def is used to define a function
✔ Functions must be called to execute
✔ Parameters receive values
✔ return sends data back
✔ Functions make code reusable