The os module provides many functions for interacting with the operating system, such as creating, moving, and deleting files and directories, and accessing environment variables.

(2) sys module

The sys module provides functionality related to the Python interpreter and system, such as the interpreter's version and path, and information related to stdin, stdout, and stderr.

(3) time module

The time module provides functions for working with time, such as getting the current time, formatting dates and times, timing, and more.

(4) datetime module

The datetime module provides more advanced date and time handling functions, such as handling time zones, calculating time difference, calculating date difference, etc.

(5) random module

The random module provides functions for generating random numbers, such as generating random integers, floating point numbers, sequences, etc.

(6) math module

The math module provides mathematical functions such as trigonometric, logarithmic, exponential, constants, etc.

(7) re module

The re module provides regular expression processing functions that can be used for text search, replacement, segmentation, etc.

(8) json module

The json module provides JSON encoding and decoding functions, which can convert Python objects to JSON format and parse Python objects from JSON format.

(9) urllib module

The urllib module provides functions for accessing web pages and processing URLs, including downloading files, sending POST requests, and handling cookies.

2. Operating system interface

(1) The os module provides many functions associated with the operating system.

>>> import os
>>> os.getcwd() # Return the current working directory
'C:\\Python34'
>>> os.chdir('/server/accesslogs') # modify the current working directory
>>> os.system('mkdir today') # Execute the system command mkdir
0

It is recommended to use the "import os" style instead of "from os import *". This ensures that os.open(), which varies from OS to OS, does not override the built-in function open().

(2) The built-in dir() and help() functions are very useful when using large modules like os:

>>> import os
>>> dir(os)
<returns a list of all module functions>
>>> help(os)
<returns an extensive manual page created from the module's docstrings>

(3) For daily file and directory management tasks, the :mod:shutil module provides an easy-to-use high-level interface:

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

3. File wildcards

The glob module provides a function for generating file listings from directory wildcard searches:

>>> import glob
>>> glob.glob('*.py')
['primes.py', 'random.py', 'quote.py']

Fourth, the command line parameters

Common utility scripts often invoke command-line arguments. These command-line parameters are stored in the argv variable of the sys module in the form of a linked list.

For example, after executing "python demo.py one two three" on the command line, you can get the following output:

>>> import sys
>>> print(sys.argv)
['demo.py', 'one', 'two', 'three']

5. Error output redirection and program termination

sys also has stdin, stdout, and stderr attributes, the latter of which can be used to display warning and error messages even when stdout is redirected.

>>> sys.stderr.write('Warning, log file not found starting a new one\n')
Warning, log file not found starting a new one

Directed termination of most scripts uses "sys.exit()".

6. Regular string matching

(1) The re module provides regular expression tools for advanced string processing.

(2) For complex matching and processing, regular expressions provide a concise and optimized solution:

>>> import re
>>> re.findall(r'\bf[a-z]*', 'which foot or hand fell fastest')
['foot', 'fell', 'fastest']
>>> re.sub(r'(\b[a-z]+) \1', r'\1', 'cat in the the hat')
'cat in the hat'

(3) If you only need simple functions, you should consider string methods first, because they are very simple and easy to read and debug:

>>> 'tea for too'.replace('too', 'two')
'tea for two'

7. Mathematics

(1) The math module provides access to the underlying C library for floating-point operations:

>>> import math
>>> math.cos(math.pi / 4)
0.70710678118654757
>>> math.log(1024, 2)
10.0

(2) random provides a tool for generating random numbers.

>>> import random
>>> random.choice(['apple', 'pear', 'banana'])
'apple'
>>> random.sample(range(100), 10)   # sampling without replacement
[30, 83, 16, 4, 8, 81, 41, 50, 18, 33]
>>> random.random()    # random float
0.17970987693706186
>>> random.randrange(6)    # random integer chosen from range(6)
4

8. Access to the Internet

There are several modules for accessing the Internet and handling network communication protocols.

Two of the simplest are urllib.request for handling data received from urls and smtplib for sending emails:

>>> from urllib.request import urlopen
>>> for line in urlopen('http://tycho.usno.navy.mil/cgi-bin/timer.pl'):
...     line = line.decode('utf-8')  # Decoding the binary data to text.
...     if 'EST' in line or 'EDT' in line:  # look for Eastern Time
...         print(line)

<BR>Nov. 25, 09:43:32 PM EST

>>> import smtplib
>>> server = smtplib.SMTP('localhost')
>>> server.sendmail('[email protected]', '[email protected]',
... """To: [email protected]
... From: [email protected]
...
... Beware the Ides of March.
... """)
>>> server.quit()

Note that the second example requires a running mail server locally.

9. Date and time

The datetime module provides both simple and complex methods for date and time manipulation.

While supporting date and time arithmetic, the implementation focuses on more efficient processing and formatting of output.

This module also supports time zone handling:

10. Data Compression

The following modules directly support common data packing and compression formats: zlib, gzip, bz2, zipfile, and tarfile.

11. Performance Metrics

Some users are interested in knowing the performance differences between different approaches to the same problem. Python provides a metrics tool that provides direct answers to these questions.

For example, exchanging elements using tuple packing and unpacking looks more attractive than using traditional methods, and timeit proves that modern methods are faster.

The :mod:profile and pstats modules provide time measurement tools for larger chunks of code relative to the fine-grainedness of timeit.

12. Test Module

One of the ways to develop high-quality software is to develop test code for each function, and to test frequently during the development process

The doctest module provides a tool that scans modules and executes tests against docstrings embedded in programs.

The test construct is as simple as cutting and pasting its output into the docstring.

It enforces documentation with user-supplied examples, allowing the doctest module to confirm that the results of the code are consistent with the documentation:

The unittest module is not as easy to use as the doctest module, but it can provide a more comprehensive set of tests in a single file:

What we have seen above is only a part of the Python3 standard library. There are many other modules that can be viewed in the official documentation for the complete standard library documentation: Python Standard Library—Python 3.11.4 Documentation

Overview of Python3 Standard Library | Novice Tutorial (18)

1. Modules in the Python3 standard library

(1) os module