Importing Modules

Introduction

A module is a Python file containing functions, classes, and variables that you can reuse across your programs. Python comes with a large standard library of built-in modules — no installation required.

Importing a Module

import math

print(math.pi)           # 3.141592653589793
print(math.sqrt(144))    # 12.0
print(math.ceil(4.2))    # 5
print(math.floor(4.9))   # 4

Importing Specific Names

from math import sqrt, pi

print(sqrt(144))   # 12.0
print(pi)          # 3.141592653589793

Aliases

import math as m
from datetime import datetime as dt

print(m.sqrt(25))
print(dt.now())

Useful Standard Library Modules

datetime — Dates and Times

from datetime import datetime, date, timedelta

today = date.today()
print(today)                        # 2024-11-01

now = datetime.now()
print(now.strftime("%d/%m/%Y %H:%M"))   # 01/11/2024 14:30

in_30_days = today + timedelta(days=30)
print(in_30_days)

os — Operating System Interaction

import os

print(os.getcwd())              # current working directory
print(os.listdir("."))          # files in current directory
os.makedirs("data", exist_ok=True)  # create a directory

pathlib — File Paths (Modern Approach)

from pathlib import Path

p = Path("data") / "employees.csv"
print(p.exists())      # True or False
print(p.suffix)        # .csv
print(p.stem)          # employees
print(p.parent)        # data

random — Random Numbers

import random

print(random.randint(1, 100))          # random integer 1–100
print(random.choice(["Alice", "Bob"])) # random item from list
random.shuffle([1, 2, 3, 4, 5])        # shuffle in place

json — JSON Data

import json

data = {"name": "Alice", "department": "Engineering", "salary": 80000}

json_string = json.dumps(data, indent=2)   # dict → JSON string
print(json_string)

parsed = json.loads(json_string)           # JSON string → dict
print(parsed["name"])

# Write to file
with open("employee.json", "w") as f:
    json.dump(data, f, indent=2)

# Read from file
with open("employee.json", "r") as f:
    loaded = json.load(f)

Practice Exercises

• Use the datetime module to print today's date in the format DD-MM-YYYY.
• Use os.listdir() to list all files in the current directory.
• Use random.choice() to pick a random item from a list of five department names.
• Read the CSV you created in the previous lesson and write its contents to a JSON file using the json module.