Day 16/100: Python Modules and import Statements

Welcome to Day 16 of the 100 Days of Python series!
Today, we're exploring modules — the building blocks of reusable code in Python.

Modules help you organize your programs, avoid repetition, and make use of thousands of pre-written utilities in the Python Standard Library and beyond.

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🧠 What is a Module?

A module in Python is simply a file that contains Python code — functions, classes, or variables — that you can reuse in other files.

Python comes with a huge collection of built-in modules (like math, random, and datetime) and also lets you create custom modules.

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🔧 How to Use a Module with import

To use a module, you use the import keyword.

Example:

import math

print(math.sqrt(16))  # Output: 4.0

You're telling Python: “Hey, I want to use the math module and its functions.”

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🎯 Common Built-in Modules

Here are a few built-in modules you’ll use often:

Module	Purpose
math	Math operations like sqrt, sin
random	Random number generation
datetime	Dates and time manipulation
os	Interact with operating system
sys	Access system-specific parameters

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🛠 Different Ways to Import

1. import module

import math
print(math.pi)

2. from module import function

from math import sqrt
print(sqrt(25))  # No need to write math.sqrt

3. from module import * (Not recommended)

from math import *
print(cos(0))  # ⚠️ May lead to namespace confusion

4. Import with Alias

import datetime as dt
print(dt.datetime.now())

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🧪 Real-World Example: Random Password Generator

import random
import string

def generate_password(length):
    chars = string.ascii_letters + string.digits
    return ''.join(random.choice(chars) for _ in range(length))

print(generate_password(10))

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🧰 Creating Your Own Module

You can write your own module by saving functions in a .py file.

math_utils.py

def square(x):
    return x * x

Use it in another file:

import math_utils

print(math_utils.square(4))  # Output: 16

Make sure both files are in the same directory, or use Python’s module path settings.

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📁 Packages vs Modules

• A module is a single .py file
• A package is a folder that contains multiple modules and an __init__.py file

You can import modules from packages like this:

from mypackage import mymodule

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⚙️ Bonus: Checking Available Functions

You can check what's inside a module using:

import math
print(dir(math))

Or use built-in help:

help(math)

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🧼 Best Practices

• ✅ Use import module or from module import specific_function
• 🚫 Avoid from module import * — it clutters the namespace
• 🧱 Break large projects into reusable modules
• 🧪 Keep utility functions in a utils.py file

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🧠 Recap

Today you learned:

• What Python modules are and why they’re useful
• How to import built-in and custom modules
• Different import methods and best practices
• Real-world use cases for math, random, and datetime
• How to build and use your own modules

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