Modules in Python

Introduction to Modules

A module is a group of statements that perform a specific task. This approach, also called divide and conquer, breaks a large task into smaller manageable modules.

What is a Module in Python?

A module is a Python file (.py) containing functions, variables, or classes. You can reuse the code by importing the module into other files.

Defining and Calling a Module

Step 1: Create a Module

# mymodule.py

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

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

Step 2: Use the Module

# main.py

import mymodule

message = mymodule.greet("Alice")
print(message)  # Output: Hello, Alice!

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

Other Ways to Import

from mymodule import greet, add
print(greet("Bob"))
print(add(2, 5))

import mymodule as mm
print(mm.greet("Eve"))

Summary of Module Syntax

Local Variables

A local variable is defined inside a function and only exists there.

Example:

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

greet()
print(message)  # Error: message is not defined

Why Use Local Variables?

• Encapsulate data
• Avoid variable interference
• Improve modularity

Local vs Global Variables

message = "Global message"

def greet():
    message = "Local message"
    print(message)

greet()         # Output: Local message
print(message)  # Output: Global message

Accessing Global Variables

message = "Hello from global scope"

def greet():
    print(message)

greet()
print(message)

Modifying Global Variable Inside Function

counter = 0

def increment():
    counter += 1  # Error: UnboundLocalError

increment()

Correct Way Using global Keyword

counter = 0

def increment():
    global counter
    counter += 1

increment()
print(counter)  # Output: 1

Passing Variables as Arguments

Example:

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

greet("Alice")
greet("Bob")

Using Variable as Argument

user_name = "Eve"

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

greet(user_name)  # Output: Hello, Eve

Better than using global:

count = 10

def increment(value):
    return value + 1

count = increment(count)
print(count)  # Output: 11

Tip: These practices help write modular, reusable, and testable code.