Python Functions – Writing Reusable & Modular Code - Learn PYTHON-BACKEND | Revochamp

Name: Python Functions – Writing Reusable & Modular Code
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What is a Function?

A function is a block of organized, reusable code that is used to perform a single, related action. Functions provide better modularity for your application and a high degree of code reusing. In Python, you define a function using the def keyword.

Defining and Calling Functions

Python uses indentation to define the body of a function. You can pass data, known as parameters, into a function, and it can return data as a result.

PythonRead-only

def greet_user(username):
    """Displays a simple greeting."""
    return f"Hello, {username}!"

# Calling the function
message = greet_user("Kishore")
print(message) # Output: Hello, Kishore!

def greet_user(username):
    """Displays a simple greeting."""
    return f"Hello, {username}!"

# Calling the function
message = greet_user("Kishore")
print(message) # Output: Hello, Kishore!

Function Parameters & Arguments

Python offers flexible ways to pass arguments. You can use positional arguments, keyword arguments, and even default values.

Default Arguments: Assign a value in the definition if none is provided during the call.
Keyword Arguments: Identify arguments by name so order doesn't matter.
Arbitrary Arguments (*args): Pass a non-keyworded, variable-length argument list.
**Keyworded Arbitrary Arguments (kwargs): Pass a keyworded, variable-length argument list.

PythonRead-only

def create_profile(name, role="Developer", **extra_info):
    profile = {"name": name, "role": role}
    profile.update(extra_info)
    return profile

user = create_profile("Kishore", location="Chennai", tech="Flutter")
# Output: {'name': 'Kishore', 'role': 'Developer', 'location': 'Chennai', 'tech': 'Flutter'}

def create_profile(name, role="Developer", **extra_info):
    profile = {"name": name, "role": role}
    profile.update(extra_info)
    return profile

user = create_profile("Kishore", location="Chennai", tech="Flutter")
# Output: {'name': 'Kishore', 'role': 'Developer', 'location': 'Chennai', 'tech': 'Flutter'}

Type Hinting (Modern Python)

Since you are familiar with Dart's static typing, you'll appreciate Python's type hinting. While not enforced by the interpreter, it makes code significantly more maintainable and helps IDEs catch bugs.

PythonRead-only

def add_numbers(a: int, b: int) -> int:
    return a + b

def add_numbers(a: int, b: int) -> int:
    return a + b

Lambda Functions (Anonymous)

Small anonymous functions can be created with the lambda keyword. They are restricted to a single expression.

PythonRead-only

square = lambda x: x * x
print(square(5)) # Output: 25

square = lambda x: x * x
print(square(5)) # Output: 25

Argument Types Comparison

Type	Syntax	Use Case
Positional	def func(a, b)	Basic, ordered inputs
Default	def func(a=1)	Optional parameters
*args	def func(*args)	Passing a variable list of items
**kwargs	def func(**kwargs)	Passing variable named settings/configs

Try it yourself

def calculate_discount(price, discount_percent=10):
    """Calculates the final price after discount."""
    savings = price * (discount_percent / 100)
    return price - savings

# Try changing the arguments!
initial_price = 1000
final = calculate_discount(initial_price, 25)

print(f"Initial: {initial_price}")
print(f"Final: {final}")

# Lambda example
multiply = lambda a, b: a * b
print(f"5 x 6 = {multiply(5, 6)}")

Test Your Knowledge

of 3

Which keyword is used to create a function in Python?

function

def

func

define

of 3

What does *args allow you to do?

Return multiple values

Pass a variable number of positional arguments

Force a function to be async

Define a private function

of 3

How do you define a default value for a parameter?

def my_func(x? = 10):

def my_func(x : 10):

def my_func(x = 10):

def my_func(default x = 10):

Frequently Asked Questions

What is 'pass' in a function?

If you want to define a function but haven't written the logic yet, you use the 'pass' keyword as a placeholder to avoid syntax errors.

Can a Python function return multiple values?

Yes! You can return a tuple (e.g., return x, y) and then destructure them when calling: a, b = my_func().

What is a docstring?

A docstring is a string literal that occurs as the first statement in a function. It's used to document what the function does and is accessible via help() or doc.

def create_profile(name, role="Developer", **extra_info): profile = {"name": name, "role": role} profile.update(extra_info) return profile user = create_profile("Kishore", location="Chennai", tech="Flutter") # Output: {'name': 'Kishore', 'role': 'Developer', 'location': 'Chennai', 'tech': 'Flutter'}

Type

Syntax

Use Case

Positional

def func(a, b)

Basic, ordered inputs

Default

def func(a=1)

Optional parameters

*args

def func(*args)

Passing a variable list of items

**kwargs

def func(**kwargs)

Passing variable named settings/configs

Try it yourself

def calculate_discount(price, discount_percent=10):
    """Calculates the final price after discount."""
    savings = price * (discount_percent / 100)
    return price - savings

# Try changing the arguments!
initial_price = 1000
final = calculate_discount(initial_price, 25)

print(f"Initial: {initial_price}")
print(f"Final: {final}")

# Lambda example
multiply = lambda a, b: a * b
print(f"5 x 6 = {multiply(5, 6)}")

Test Your Knowledge

of 3

Which keyword is used to create a function in Python?

function

def

func

define

of 3

What does *args allow you to do?

Return multiple values

Pass a variable number of positional arguments

Force a function to be async

Define a private function

of 3

How do you define a default value for a parameter?

def my_func(x? = 10):

def my_func(x : 10):

def my_func(x = 10):

def my_func(default x = 10):

Frequently Asked Questions

What is 'pass' in a function?

If you want to define a function but haven't written the logic yet, you use the 'pass' keyword as a placeholder to avoid syntax errors.

Can a Python function return multiple values?

Yes! You can return a tuple (e.g., return x, y) and then destructure them when calling: a, b = my_func().

What is a docstring?

A docstring is a string literal that occurs as the first statement in a function. It's used to document what the function does and is accessible via help() or doc.

Python Functions – Writing Reusable & Modular Code

Python Functions – Writing Reusable & Modular Code

What is a Function?

Defining and Calling Functions

Function Parameters & Arguments

Type Hinting (Modern Python)

Lambda Functions (Anonymous)

Argument Types Comparison

Try it yourself

Test Your Knowledge

Frequently Asked Questions

Need help?

Python Functions – Writing Reusable & Modular Code

Python Functions – Writing Reusable & Modular Code

What is a Function?

Defining and Calling Functions

Function Parameters & Arguments

Type Hinting (Modern Python)

Lambda Functions (Anonymous)

Argument Types Comparison

Try it yourself

Test Your Knowledge

Frequently Asked Questions

Need help?