String Operations and Methods

What is a Function ?

A function is a block of code that performs a specific task and can be reused multiple times in a program.

Without functions, programmers would need to write the same code again and again, which makes programs longer and harder to manage.

Example without function:

print("Hello Aman")
print("Hello Rahul")
print("Hello Priya")

Using function:

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

greet("Aman")
greet("Rahul")
greet("Priya")

Defining Functions

In Python, functions are defined using the def keyword.

Basic Syntax

def function_name():
    # code block

Example: Simple Function , greet( ) will be called by and the value will be printed.

def greet():            # function definiton
    print("Welcome to Python Programming")

greet()                    # function call

Output:

Welcome to Python Programming

Key Points While Defining Functions

• Use def keyword
• Function name should be meaningful
• Parentheses () are required
• Colon : is used after function declaration
• Proper indentation is mandatory

Function Naming Rules

• Must start with a letter or underscore
• Cannot use keywords like if, for, while
• Should follow lowercase naming convention
• Use descriptive names like calculate_sum()

Parameters and Arguments

Functions can take input values called parameters. These inputs help functions perform operations dynamically.

Arguments are the values you pass into a function call when you call it.

Function with Parameters

def greet(name):                     # name is parameter
    print("Hello", name)

greet("Aman")                    # value Aman will be passed to parameter name

Output:

Hello Aman

Multiple Parameters

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

add(5, 3)

8

Positional Arguments

In this values are passed in correct order of parameters.

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

student("Aman", 20)              # name , age : Aman , 20

Aman 20

Keyword Arguments

Arguments are passed using parameter names.

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

student(age=20, name="Aman")

Aman 20

Default Arguments

Default values are assigned if no value is provided.

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

greet()
greet("Rahul")

Hello Guest
Hello Rahul

Variable-Length Arguments

It is used when number of inputs is unknown while writing function definition.

def add(*numbers):
    print(sum(numbers))

add(1, 2, 3, 4)

Return Values in Functions

Functions can return calculated values using the return keyword.

Example:

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

result = add(10, 5)        # get the calculated value in result variable
print(result)

Output:

15

Returning Multiple Values

def operations(a, b):
    return a + b, a - b

x, y = operations(10, 5)
print(x, y)

Built-in Functions

Built-in functions are pre-defined functions available in Python.

Examples:

print("Hello")
print(len("Python"))              # we can directly use functions in print( )
print(type(10))
print(max(5, 10, 20))

Hello
6
<class 'int'>
20

These functions are ready to use without defining them.

Common Built-in Functions

User-Defined Functions

User-defined functions are created by programmers to perform specific tasks.

Example: calculate the square of the value provided

def square(x):
    return x * x
print(square(4))

Output:

16

Scope of Variables

Variables inside functions have limited scope.

Local Variable

def test():
    x = 10
    print(x)
test()                 # x will be printed
print(x)             # error because x is not defined or defined in a function definition

10
NameError: name 'x' is not defined

Global Variable

x = 5
def show():
    print(x)             # value of x will be printed because it is defined outside function
show()

5

Recursive Functions

A function that calls itself is called recursion.

def factorial(n):
    if n == 1:
        return 1
    return n * factorial(n-1)
print(factorial(5))

120

Practical Examples

Example 1: Even or Odd

def check_even(num):
    if num % 2 == 0:
        return "Even"
    return "Odd"
print(check_even(7))

Odd

Example 2: Calculator

def calculator(a, b):
    return a + b, a - b, a * b
print(calculator(10, 5))

(15, 5, 50)

Example 3: Find Maximum

def find_max(a, b):
    if a > b:
        return a
    return b
print(find_max(10, 20))

20