Python Libraries

os

in-built library that provides functions for interacting with the operating system
Use case: File and directory management, environment variables, etc.

Function	Description	Example
`os.path.join()`	Joins one or more path components intelligently.	`os.path.join("folder", "subfolder", "file.txt")`
`os.listdir()`	Returns a list of the entries in the directory given by path.	`os.listdir("folder")`
`os.mkdir()`	Creates a directory named path with numeric mode mode.	`os.mkdir("new_folder")`
`os.rename()`	Renames the file or directory src to dst.	`os.rename("old_name.txt", "new_name.txt")`
`os.rmdir()`	Removes a directory named path.	`os.rmdir("folder")`
`os.remove()`	Removes (deletes) the file path.	`os.remove("file.txt")`
`os.path.getsize()`	Returns the size of path in bytes.	`os.path.getsize("file.txt")`
`os.system()`	Executes the command (a string) in a subshell.	`os.system("ls -l")`
`os.path.exists()`	Returns True if path refers to an existing path.	`os.path.exists("file.txt")`

Commonly Used Functions in OS Library

random

in-built library that provides functions related to random operations
Use case: Random number generation, shuffling data, etc.

Function	Description	Example
`random.random()`	Returns a random float number in the range [0.0, 1.0).	`random.random()`
`random.randint(a, b)`	Returns a random integer N in range [a, b].	`random.randint(1, 10)`
`random.choice(seq)`	Returns a random element from the sequence seq.	`random.choice([1, 2, 3, 4, 5])`
`random.shuffle(x)`	Shuffles the sequence x in place.	`my_list = [1, 2, 3, 4, 5]; random.shuffle(my_list)`
`random.sample(seq, k)`	Returns a k length list of unique elements from sequence.	`random.sample([1, 2, 3, 4, 5], 3)`
`random.seed(value)`	Initializes the random number generator with a seed value.	`random.seed(42)`

Commonly Used Functions in random Library

math

in-built library that provides functions for mathematical operations
Use case: Mathematical calculations, trigonometric functions, etc.

Function	Description	Example
`math.floor(x)`	Returns the largest integer less than or equal to x.	`math.floor(3.7)`
`math.ceil(x)`	Returns the smallest integer greater than or equal to x.	`math.ceil(3.2)`
`math.sqrt(x)`	Returns the square root of x.	`math.sqrt(16)`
`math.pow(x, y)`	Returns x raised to the power of y.	`math.pow(2, 3)`
`math.sin(x)`	Returns the sine of x radians.	`math.sin(math.pi / 2)`
`math.radians(x)`	Converts angle x from degrees to radians.	`math.radians(180)`
`math.pi`	Mathematical constant π (pi), approximately 3.14159.	`math.pi`
`math.log(x, base)`	Returns the logarithm of x to the given base.	`math.log(100, 10)`
`math.factorial(n)`	Returns the factorial of n.	`math.factorial(5)`
`math.gcd(a, b)`	Returns the greatest common divisor of a and b.	`math.gcd(12, 18)`
`math.lcm(a, b)`	Returns the least common multiple of a and b.	`math.lcm(12, 18)`

Commonly Used Functions in math Library

mailerpy

third-party library that provides functions for sending emails using Python.
Installed as: pip install mailerpy.
First, Generate secure gmail password. Then set it as environment variable EMAIL_PASSWORD.

Example:

from mailerpy import Mailer import os password = os.getenv("EMAIL_PASSWORD") mailer = Mailer("smtp.gmail.com", 587, "your_email", password) to_emails = ["[email protected]", "[email protected]"], subject = "Test Email from mailerpy" body = "Hello, this is a test email sent using mailerpy library in Python." attachment_list = [r'C:\Desktop\test.txt', 'test2.txt'] mailer.send_mail(to_emails, subject, body, attachments=attachment_list)

datetime

in-built library that provides functions for manipulating dates and times.
Use case: Date and time manipulation, formatting, etc.
We often use date and datetime submodule

Function	Description	Example
`datetime.now()`	Returns the current local date and time.	`datetime.now()`
`date.today()`	Returns the current local date.	`date.today()`
`dt_obj.strftime(format)`	Formats a datetime object into a string.	`dt_obj.strftime("%Y-%m-%d")`
`.strptime(string, format)`	Parses a string into a datetime object.	`datetime.strptime("2023-01-01", "%Y-%m-%d")`
`dt_obj + timedelta(days=n)`	Adds n days to a datetime object.	`dt_obj + datetime.timedelta(days=7)`
`d2 - d1`	Subtracts two dates, returning a timedelta.	`d2 - d1`

Commonly Used Functions in datetime Library

Common Datetime Formats

Format	Description	Example
`%Y`	Year	`2023`
`%m`	Month	`01`
`%d`	Day	`01`
`%H`	Hour	`12`
`%M`	Minute	`34`
`%S`	Second	`56`
`%B`	Full Month Name	`January`
`%b`	Abbreviated Month Name	`Jan`
`%A`	Full Weekday Name	`Monday`
`%a`	Abbreviated Weekday Name	`Mon`
`%p`	AM or PM	`AM`
`%j`	Day of the Year	`001`
`%U`	Week of the Year (Sunday as the First Day)	`01`
`%W`	Week of the Year (Monday as the First Day)	`01`
`%w`	Day of the Week	`0` (Sunday)
`%-d`	Day of the Month (no leading zero)	`1`
`%-m`	Month (no leading zero)	`1`
`%y`	Year without century	`23`

Common Datetime Formats and their Notation

requests

third-party library that allows you to send HTTP requests easily.
Installed as: pip install requests.
Supports various HTTP methods like GET, POST, PUT, DELETE, etc.

Example:

import requests response = requests.get("https://www.google.com") print(response.status_code) # Output: 200 print(response.json()) # Output: JSON response from Google print(response.text) # Output: HTML content of the page print(response.headers) # Output: Response headers

beautifulsoup

third-party library that allows you to parse HTML and XML documents.
Installed as: pip install beautifulsoup4.
Has methods like find(), find_all(), select(), etc. to navigate and search the parse tree.

Example:

from bs4 import BeautifulSoup import requests response = requests.get("https://www.google.com") soup = BeautifulSoup(response.text, "html.parser") print(soup.title.text)

pandas

third-party library that provides data structures and data analysis tools.
Installed as: pip install pandas.

Example:

import pandas as pd df = pd.read_csv(file_path) print(df.head()) print(df.describe()) filter_mask = (df["LTP"] > 150) & (df["LTP"] < 300) filtered_data = df[filter_mask] print(filtered_data.head()) filtered_data.to_csv("filtered_data.csv")

matplotlib

third-party library that provides functions for creating static, animated, and interactive visualizations in Python.
Installed as: pip install matplotlib.

Example:

import matplotlib.pyplot as plt # Creating a simple line plot x = [1, 2, 3, 4, 5] y = [10, 20, 25, 30, 40] plt.plot(x, y) plt.title("Line Plot") plt.xlabel("X-axis") plt.ylabel("Y-axis") plt.show()