Working With Functions

 📘 Working with Functions 

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🔹 1. Introduction to Functions

📌 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 use functions.

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📌 Advantages of Functions

• Code reusability
• Reduces redundancy
• Improves readability
• Easy debugging
• Modular programming

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📌 Types of Functions

1. Built-in functions → print(), len()
2. User-defined functions
3. Recursive functions
4. Lambda (anonymous) functions

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🔹 2. Creating User-Defined Functions

📌 Syntax:

def function_name(parameters):

    # body of function

    return value

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📌 Example:

def greet():

    print("Hello Students")

👉 Calling function:

greet()

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🔹 3. Function Arguments (VERY IMPORTANT)

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➤ 1. Required (Positional) Arguments

• Must be passed in correct order

def add(a, b):

    print(a + b)

             add(5, 3)

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➤ 2. Default Arguments

• Assign default value

def greet(name="Guest"):

    print("Hello", name)

greet()

greet("Bhav")

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➤ 3. Keyword Arguments

• Values passed using parameter names

                add(b=10, a=5)

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➤ 4. Variable Length Arguments

🔸 *args (Non-keyword)

def total(*nums):

    print(sum(nums))

    total(1,2,3,4)

🔸 **kwargs (Keyword arguments)

def info(**data):

    print(data)

    info(name="Bhav", age=20)

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🔹 4. Return Statement

📌 Purpose:

• Returns result to caller
• Ends function execution

    def square(x):
        return x*x

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📌 Multiple Return Values

def calc(a, b):

    return a+b, a-b

    sum1, diff = calc(10, 5)

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🔹 5. Scope of Variables

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📌 Local Variable

• Defined inside function
• Accessible only within function

def demo():

    x = 10

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📌 Global Variable

• Defined outside function
• Accessible everywhere

x = 20

def show():

    print(x)

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📌 Using global Keyword

x = 5

def change():

    global x

    x = 10

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🔹 6. Recursion (IMPORTANT)

📌 Definition:

    Function calling itself

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📌 Example: Factorial

def factorial(n):

    if n == 1:

        return 1

    return n * factorial(n-1)

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📌 Key Points:

• Must have base condition
• Otherwise → infinite recursion

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🔹 7. Lambda Functions (Anonymous Functions)

📌 Definition:

        Small one-line function without name

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📌 Syntax:

    lambda arguments: expression

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📌 Example:

square = lambda x: x*x

print(square(5))

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📌 Use Cases:

• Short operations
• Used with map(), filter()

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🔹 8. Built-in Functions (Common)

Function	Use
len()	Length
sum()	Total
max()	Maximum
min()	Minimum

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🔹 9. Functions with Lists

def total(lst):

    return sum(lst)

    print(total([1,2,3]))

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🔹 10. Functions with Strings

def count_vowels(s):

    count = 0

    for ch in s:

        if ch.lower() in "aeiou":

            count += 1

    return count

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🔹 11. Passing Arguments (Important Concept)

📌 Call by Value vs Reference (Python Concept)

• Immutable → passed by value (int, string)
• Mutable → passed by reference (list)

def modify(lst):

    lst.append(100)

l = [1,2]

modify(l)

print(l)

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🔹 12. Docstring in Functions

📌 Purpose:

• Describe function

def add(a, b):

    """This function returns sum"""

    return a + b

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🔹 13. Good Programming Practices

✔ Use meaningful function names

✔ Keep functions short

✔ Use comments/docstrings

✔ Avoid global variables

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🧠 Important Viva Questions

1. What is a function?
2. Difference between parameter and argument?
3. What is recursion?
4. What is lambda function?
5. Difference between local and global variable?
6. What is default argument?
7. What is *args and **kwargs?