17Introduction to the Python Standard Library

What Is the Python Standard Library?

The Python Standard Library (PSL) is a collection of ready-made modules that come bundled with Python. Instead of writing everything from scratch, you can import these modules and save development time while writing clean, readable code.

Why Use the Standard Library?

• No need to install extra packages
• Reliable and well-tested
• Cross-platform (works on Windows, macOS, Linux)
• Covers common use cases in real-world development

Commonly Used Standard Library Modules

1. os – Interact with Operating System

import os
print(os.getcwd())  # Get current working directory
print(os.listdir())  # List files in current folder

2. sys – Access System-Specific Info

import sys
print(sys.version)  # Python version
print(sys.path)     # Module search path

3. math – Mathematical Functions

import math
print(math.sqrt(49))
print(math.pi)
print(math.factorial(6))

4. datetime – Work with Dates & Time

from datetime import datetime
now = datetime.now()
print(now.strftime("%Y-%m-%d %H:%M:%S"))

5. random – Generate Randomness

import random
print(random.randint(1, 10))  # Random integer
print(random.choice(['apple', 'banana', 'mango']))

6. statistics – Basic Data Statistics

import statistics as stats
data = [1, 2, 3, 4, 5, 6]
print(stats.mean(data))
print(stats.median(data))

7. collections – Advanced Data Structures

from collections import Counter
nums = [1, 2, 2, 3, 3, 3, 4]
print(Counter(nums))  # Count occurrences of each element

Standard Library vs Installing External Packages

Official Python Standard Library Documentation

Mini Project Step

Extend your Calculator project by adding a `statistics` utility file that uses the `statistics` module to compute mean, median, and mode. Also use `datetime` to log when each calculation happens.