Hello Friends,

Python Functions

A function in Python is a reusable block of code that performs a specific task. Functions help reduce code duplication, improve readability, and make programs easier to maintain.

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Why Use Functions?

• Reuse code multiple times
• Make programs modular
• Improve readability and maintenance
• Reduce errors

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Syntax of a Function

def function_name(parameters):
    statements
    return value

• def – keyword to define a function
• function_name – name of the function
• parameters – inputs to the function
• return – sends result back to caller

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Example 1: Simple Function

def greet():
    print("Welcome to Python Functions")

greet()

Output:

Welcome to Python Functions

Explanation:
The function greet() prints a message when called.

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Example 2: Function with Parameters

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

greet_user("Chandan")

Output:

Hello Chandan

Explanation:
The function accepts a parameter name and prints a personalized message.

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Example 3: Function with Return Value

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

result = add(10, 20)
print(result)

Output:

30

Explanation:
The function returns the sum of two numbers.

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Example 4: Default Arguments

Default arguments are used when no value is passed.

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

greet()
greet("Amit")

Output:

Hello Guest
Hello Amit

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Example 5: Keyword Arguments

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

student_info(age=25, name="Rahul")

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Example 6: Arbitrary Arguments (*args)

*args allows passing multiple values.

def total_marks(*marks):
    total = 0
    for m in marks:
        total += m
    return total

print(total_marks(70, 80, 90))

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Example 7: Arbitrary Keyword Arguments (**kwargs)

**kwargs allows passing key-value pairs.

def employee_details(**details):
    for key, value in details.items():
        print(key, ":", value)

employee_details(name="Ravi", role="Tester", salary=50000)

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Example 8: Function Inside a Function

def outer_function():
    def inner_function():
        print("Inner Function Executed")
    inner_function()

outer_function()

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Example 9: Lambda Function

Lambda functions are small anonymous functions.

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

Output:

25

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Real-Life Example

Checking pass or fail:

def check_result(marks):
    if marks >= 40:
        return "Pass"
    else:
        return "Fail"

print(check_result(55))

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Common Mistakes

• Forgetting to call the function
• Incorrect indentation
• Using return incorrectly
• Mismatch in parameters and arguments

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Summary

• Functions help reuse code
• Functions can take parameters and return values
• Supports default, keyword, *args, **kwargs
• Lambda functions are short functions