[Ch 9] Everything About Python Standard Library from the Official Documentation

Overview

This document is a more easily understandable summary of the contents of 10. Brief Tour of Standard Library in the official Python v3.13 Tutorial.

1. Operating System Interface

1.1 `os` Module


import os
print(os.getcwd())
os.chdir('/server/accesslogs') 
os.system('mkdir today')


C:\\path\\to\\folder\\repository

The os module provides various functions for interacting with the operating system.

When importing the module, be sure to use the import os format rather than from os import *.

This is to prevent conflicts between Python's built-in open() function and the os module's os.open() function.


import os
print(dir(os))
print(help(os))


['DirEntry', 'EX_OK', 'F_OK', 'GenericAlias', ...]
Help on module os:

NAME
    os - OS routines for NT or Posix depending on what system we're on.
...

You can also use the dir or help functions to get detailed information about a module.

dir returns a list of all the content that the module exports, and help creates a manual for the module based on its docstring.

1.2 `shutil` Module


import shutil
shutil.copyfile('data.db', 'archive.db')
shutil.move('/build/executables', 'installdir')

The shutil module provides functions for easily controlling files and folders.

2. File Wildcards


import glob
print(glob.glob('*.py'))


['code1.py', 'code2.py', 'tmp.py']

The glob module provides a function for finding files using wildcards.

3. Command-Line Arguments

3.1 `sys.argv`


# demo.py file
import sys
print(sys.argv)


PS C:\\path\\to\\folder> python demo.py 1 Hello True
['demo.py', '1', 'Hello', 'True']

The sys module allows you to receive values passed as arguments when running a Python file through sys.argv.

3.2 `argparse` Module


# demo.py file
import argparse

parser = argparse.ArgumentParser(
    prog='top',
    description='Show top lines from each file')
parser.add_argument('filenames', nargs='+')
parser.add_argument('-l', '--lines', type=int, default=10)
args = parser.parse_args()
print(args)


PS C:\\path\\to\\folder> python demo.py 
usage: top [-h] [-l LINES] filenames [filenames ...]
top: error: the following arguments are required: filenames


PS C:\\path\\to\\folder> python demo.py file.txt -l 3
Namespace(filenames=['file.txt'], lines=3)

The argparse module allows for more advanced handling of command-line arguments for Python files.

4. Error Messages and Program Termination


import sys
sys.stderr.write('An error has occurred.')
sys.exit(1)


An error has occurred.

The sys module also allows you to write error messages to stderr.

The sys.exit function stops the execution of the program and can be assigned a specific exit code.

An exit code of 1 indicates an abnormal termination.

5. Regex Matching


import re

print(re.findall(r'\\bf[a-z]*', 'which foot or hand fell fastest'))
print(re.sub(r'(\\b[a-z]+) \\1', r'\\1', 'cat in the the hat'))
print('tea for too'.replace('too', 'two'))


['foot', 'fell', 'fastest']
cat in the hat
tea for two

By using the re module, you can perform string matching, searching, and substitution with regular expressions.

6. Mathematics

6.1 `math` Module


import math
print(math.cos(math.pi / 4))
print(math.log(1024, 2))


0.7071067811865476
10.0

The math module supports basic mathematical functions and constants.

The supported functions and constants follow the C language standard.

6.2 `random` Module


import random

print(random.choice(['apple', 'pear', 'banana']))
print(random.sample(range(100), 10))
print(random.random())
print(random.randrange(6))


apple
[14, 40, 78, 99, 21, 85, 18, 64, 54, 27]
0.9291587367817131
4


banana
[81, 44, 9, 88, 87, 17, 90, 24, 29, 66]
0.5187855811434525
3

The random module supports a wide range of things related to randomness and probability.

Unlike C, it does not require initial seed initialization to use random numbers.

6.3 `statistics` Module


import statistics

data = [2.75, 1.75, 1.25, 0.25, 0.5, 1.25, 3.5]

print(statistics.mean(data))
print(statistics.median(data))
print(statistics.variance(data))


1.6071428571428572
1.25
1.3720238095238095

The statistics module supports many things related to statistics.

7. Internet Access

7.1 `urllib` Package


from urllib.request import urlopen

with urlopen('https://timeapi.io/api/time/current/zone?timeZone=Etc%2FUTC') as response:
    data = response.read()
    data = data.decode('utf-8')
    print(data)


{"year":2025,"month":7,"day":26,"hour":8,"minute":27,"seconds":47,"milliSeconds":397,"dateTime":"2025-07-26T08:27:47.3977202","date":"07/26/2025","time":"08:27","timeZone":"Etc/UTC","dayOfWeek":"Saturday","dstActive":false}

The urllib package contains several modules related to URLs.

The urllib.request module allows you to make URL requests, mainly HTTP requests.

7.2 `smtplib` Module


import smtplib

server = smtplib.SMTP('localhost')
server.sendmail('soothsayer@example.org', 'jcaesar@example.org',
"""To: jcaesar@example.org
From: soothsayer@example.org

Beware the Ides of March.
"""
)
server.quit()

The smptlib module allows you to create an SMTP client and send emails.

8. Dates and Times


from datetime import date

now = date.today()
print(now)
print(now.strftime("%m-%d-%y. %d %b %Y is a %A on the %d day of %B."))

birthday = date(1964, 7, 31)
age = now - birthday
print(age.days)


2025-07-24
07-24-25. 24 Jul 2025 is a Thursday on the 24 day of July.
22273

The datetime module supports various functions related to dates and times.

In addition to dates and times, it also supports date output formatting and timezones.

9. Data Compression


import zlib

s = b'witch which has which witches wrist watch'
print(len(s))

t = zlib.compress(s)
print(len(t))

print(zlib.decompress(t))
print(zlib.crc32(s))


41
37
b'witch which has which witches wrist watch'
226805979

Python supports modules such as zlib, gzip, bz2, lzma, zipfile, and tarfile for data compression.

10. Performance Measurement


from timeit import Timer

print(Timer('t=a; a=b; b=t', 'a=1; b=2').timeit())
print(Timer('a,b = b,a', 'a=1; b=2').timeit())


0.017941600002814084
0.009880399997200584

When you need to measure the performance of a program in Python, you can use a module like timeit.

The timeit module allows you to measure the time it takes to execute code written as a string.

For larger code blocks, you can use modules like profile and pstats.

11. Testing

11.1 `doctest` Module


def average(values):
    """Computes the arithmetic mean of a list of numbers.

    >>> print(average([20, 30, 70]))
    40.0
    """
    return sum(values) / len(values)

import doctest
print(doctest.testmod())


TestResults(failed=0, attempted=1)

The doctest module allows you to easily run tests and see the results based on the program's docstring.

11.2 `unittest`


import unittest

def average(values):
    return sum(values) / len(values)

class TestStatisticalFunctions(unittest.TestCase):
    def test_average(self):
        self.assertEqual(average([20, 30, 70]), 40.0)
        self.assertEqual(round(average([1, 5, 7]), 1), 4.3)
        with self.assertRaises(ZeroDivisionError):
            average([])
        with self.assertRaises(TypeError):
            average(20, 30, 70)

unittest.main()


.
---------------------------------------------------------------------- 
Ran 1 test in 0.000s

OK

The unittest module provides tools for conducting unit tests.

12. “Batteries Included” Philosophy

Python promotes the “Batteries Included” philosophy as the motto for its standard modules.

“Batteries Included” means that most tasks can be performed with only the standard modules, without the need for additional modules.

Although we have briefly looked at various standard modules in this document, Python supports over 200 standard modules.

As such, Python follows the “Batteries Included” philosophy of minimizing the use of external packages by supporting the vast majority of functionalities as built-in modules.

Reference

[1] Python Software Foundation. "10. Brief Tour of the Standard Library" The Python Tutorial, version 3.13, Python Software Foundation, 2024, https://docs.python.org/3.13/tutorial/stdlib Accessed 26 July 2025.

[Ch 9] Everything About Python Standard Library from the Official Documentation

[Ch 9] Everything About Python Standard Library from the Official Documentation

1. Operating System Interface

1.1 os Module

1.2 shutil Module

2. File Wildcards

3. Command-Line Arguments

3.1 sys.argv

3.2 argparse Module

4. Error Messages and Program Termination

5. Regex Matching

6. Mathematics

6.1 math Module

6.2 random Module

6.3 statistics Module

7. Internet Access

7.1 urllib Package

7.2 smtplib Module

8. Dates and Times

9. Data Compression

10. Performance Measurement

11. Testing

11.1 doctest Module

11.2 unittest

12. “Batteries Included” Philosophy

Reference

1.1 `os` Module

1.2 `shutil` Module

3.1 `sys.argv`

3.2 `argparse` Module

6.1 `math` Module

6.2 `random` Module

6.3 `statistics` Module

7.1 `urllib` Package

7.2 `smtplib` Module

11.1 `doctest` Module

11.2 `unittest`