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Python Course

Python Standard Libraries

1. string- Basic Operations

import string

# predefined string constants can be used in common scenarios
print(string.ascii_letters) # abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
print(string.digits) # 0123456789
print(string.hexdigits) # 0123456789abcdefABCDEF
print(string.punctuation) # !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

intro_text = "With over 18 years of experience in IT, I specialize in software development and freelancing, offering tailored solutions that meet the unique needs of your business."
print(intro_text)

print(intro_text.isalnum()) # False
print(intro_text.isalpha()) # False

# startswith and endswith
print(intro_text.startswith("With")) # True
print(intro_text.startswith("The")) # False
print(intro_text.endswith("business.")) # True

# find, rfind and in
print(intro_text.find("18")) # 10
print(intro_text.rfind("18")) # 10
print("18" in intro_text) # True

# replace
new_intro_text = intro_text.replace("and freelancing", ", freelancing and trainer")
print(new_intro_text)

# count
print(intro_text.count("in")) # 5

# lower and upper
print(intro_text.lower())
print(intro_text.upper())

# split and join
print(intro_text.split(" "))
letters = ["a","b","c","d"]
print(", ". join(letters)) # a, b, c, d

2. datetime – Working with Dates and Times

The datetime module provides classes for manipulating dates and times.

Common Classes:

  • datetime.date: Handles date (year, month, day)
  • datetime.time: Handles time (hour, minute, second)
  • datetime.datetime: Combines date and time
  • datetime.timedelta: Represents duration (difference between dates/times)
from datetime import date, datetime, timedelta

# Current date and time
now = datetime.now()
print("Now:", now)  # Now: 2023-07-09 10:09:23.635460

# Specific date
d = date(2023, 7, 9)
print("Specific date:", d) # Specific date: 2023-07-09

# Date difference
delta = date(2023, 12, 25) - date(2023, 7, 9)
print("Days until Christmas:", delta.days) # Days until Christmas: 169

# Add 10 days to today
future = date.today() + timedelta(days=10)
print("Date after 10 days:", future) # Date after 10 days: 2023-07-19

# Current UTC time 
utc_now = datetime.utcnow()
formatted_utc = utc_now.isoformat(timespec='seconds')
print("Current UTC time:", formatted_utc) # Current UTC time: 2023-07-09T10:09:23

3. calendar – Calendar-related Functions

The calendar module lets you output calendars and check for leap years, weekdays, etc.

Useful Functions:

  • calendar.month(year, month): Returns a calendar for a month
  • calendar.isleap(year): Checks if the year is a leap year
  • calendar.weekday(year, month, day): Returns weekday index (0=Monday)
  • calendar.monthcalendar(year, month): Matrix of the month’s calendar
import calendar

# Print calendar for July 2023
print(calendar.month(2023, 7))

# Is 2024 a leap year?
print("Is 2024 leap year?", calendar.isleap(2024))

# Weekday of a specific date
print("Weekday of 9 July 2023:", calendar.weekday(2023, 7, 9))

4. urllib.request – Fetching Data from the Web

The urllib.request module helps in opening and reading URLs.

Common Functions:

  • urllib.request.urlopen(url): Opens the URL
  • read(): Reads the response
  • decode(): Converts bytes to string
import urllib.request

# open a connection to a URL using urllib2
web_url = urllib.request.urlopen("https://www.praveenoruganti.in")

# get the result code and print it
print ("Result code:", web_url.getcode())

# read the data from the URL and print it
data = web_url.read()
print("Webpage content:")
print(data)

5. json Module

The json module in Python allows you to encode (dump) and decode (load) JSON data. It converts JSON strings into Python objects, and vice versa.

import urllib.request
import json

try:
    web_url = urllib.request.urlopen("http://uselessfacts.jsph.pl/api/v2/facts/random")
    print("Result code:", web_url.getcode())

    data = web_url.read()
    theJSON = json.loads(data)

    print("Random Fact:", theJSON["text"])
except Exception as e:
    print("Error fetching or parsing JSON:", e)

6. xml.dom.minidom Module

The xml.dom.minidom module in Python — a lightweight Document Object Model (DOM) parser for working with XML.

samplexml.xml

<skills>
    <skill name="Python"/>
    <skill name="JavaScript"/>
    <skill name="HTML"/>
</skills>

xml_parsing.py

import xml.dom.minidom

try:
    doc = xml.dom.minidom.parse("samplexml.xml")

    print("Document Node:", doc.nodeName)
    print("Root Tag:", doc.firstChild.tagName)

    skills = doc.getElementsByTagName("skill")
    print("Skill count:", skills.length)

    for skill in skills:
        print("Skill:", skill.getAttribute("name"))
except Exception as e:
    print("Error loading or parsing XML:", e)

7. os – Interacting with the Operating System

The os module provides a way to use operating system-dependent functionality like reading or writing to the file system.

Key Features:

  • os.getcwd(): Get current working directory
  • os.listdir(): List files/directories
  • os.mkdir(), os.remove(), os.rename()
  • os.path: Common path operations
import os

# Get current working directory
print("Current directory:", os.getcwd())

# List files in the current directory
print("Files:", os.listdir())

# Join paths safely
full_path = os.path.join(os.getcwd(), "test.txt")
print("Full path:", full_path)

8. sys – System-Specific Parameters and Functions

Useful for interacting with the Python interpreter and command-line arguments.

Key Features:

  • sys.argv: Access command-line arguments
  • sys.exit(): Exit script
  • sys.path: View module search paths
import sys

print("Script name:", sys.argv[0])
print("Python version:", sys.version)

9. math – Mathematical Functions

Provides access to basic mathematical functions and constants.

Key Features:

  • math.sqrt(), math.pow(), math.factorial()
  • Constants: math.pi, math.e
import math

print("Square root of 25:", math.sqrt(25))
print("Pi:", math.pi)

10. random – Generating Random Numbers

Useful for simulations, games, or any situation needing randomization.

Key Features:

  • random.randint(a, b)
  • random.choice(list)
  • random.shuffle(list)
import random

print("Random number:", random.randint(1, 10))
print("Random choice:", random.choice(['Praveen', 'Kiran', 'Praneeth']))

11. re – Regular Expressions

Enables powerful pattern matching and text processing.

Key Features:

  • re.search(), re.match(), re.findall()
  • Pattern substitution with re.sub()
import re

pattern = r"\d+"
text = "There are 24 hours in a day."

matches = re.findall(pattern, text)
print("Found numbers:", matches)