Python Functions

Functions are reusable blocks of code that perform a specific task. They help organize code, reduce repetition, and improve readability.

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What is a Function?

A function is a named sequence of statements that performs a computation. You define a function once and can use it as many times as needed.

Defining a Function

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

Calling a Function

greet()  # Output: Hello, world!

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Why Use Functions?

• Reusability: Write code once and use it multiple times.
• Organization: Break programs into smaller, manageable parts.
• Maintainability: Easier to debug and update code.
• Avoid Repetition: Reduces duplicate code.

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Function with Parameters

Functions can accept inputs, known as parameters.

def greet(name):
    print(f"Hello, {name}!")

Example:

greet("Alice")   # Output: Hello, Alice!
greet("Bob")     # Output: Hello, Bob!

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Function with Return Value

Functions can return values using the return statement.

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

Example:

result = add(3, 4)
print(result)    # Output: 7

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Default Parameters

You can provide default values for parameters.

def greet(name="Guest"):
    print(f"Hello, {name}!")

Example:

greet()           # Output: Hello, Guest!
greet("Diana")    # Output: Hello, Diana!

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Keyword and Positional Arguments

Python supports both positional and keyword arguments.

def describe_pet(animal, name):
    print(f"I have a {animal} named {name}.")

Example:

describe_pet("dog", "Buddy")                   # Positional
describe_pet(name="Whiskers", animal="cat")    # Keyword

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Returning Multiple Values

Functions can return multiple values as a tuple.

def get_coordinates():
    x = 5
    y = 10
    return x, y

a, b = get_coordinates()
print(a, b)  # Output: 5 10

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Scope of Variables

Variables defined inside a function are local to that function.

def example():
    local_var = "I am local"
    print(local_var)

example()
# print(local_var)  # This would raise an error

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Summary

Feature	Description
def keyword	Used to define a function
return statement	Sends a result back to the caller
Parameters	Input values passed to a function
Default values	Optional values for parameters
Reusability	Functions reduce code duplication
Scope	Local vs Global variable access

Understanding how to write and use functions is crucial for building efficient and modular Python programs.