| Operating System Interface |
the os module
provides dozens of functions for interacting with the operating system
>>> import os
>>> os.getcwd() # Return the current working directory
'C:\\Python313'
>>> os.chdir('/server/accesslogs') # Change current working directory
>>> os.system('mkdir today') # Run the command mkdir in the system shell
0
use the import os style instead of from os import *this will keep os.open() from shadowing the built-in open() function which operates much differently built-in dir() and help() functions are useful as interactive aids for working with 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>for file and directory management tasks the shutil module provides a higher level interface which is easier to use >>> import shutil
>>> shutil.copyfile('data.db', 'archive.db')
'archive.db'
>>> shutil.move('/build/executables', 'installdir')
'installdir'
|
| File Wildcards |
the glob module
provides a function for making file lists from directory wildcard searches
>>> import glob
>>> glob.glob('*.py')
['primes.py', 'random.py', 'quote.py']
|
| Command Line Arguments |
|
common utility scripts can need to process command line arguments these arguments are stored in the sys module's argv attribute as a list # File demo.py >>> import sys >>> print(sys.argv) ['demo.py', 'one', 'two', 'three']the argparse module provides a more sophisticated mechanism to process command line arguments script below extracts one or more filenames and an optional number of lines to be displayed 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)
|
| Error Output Redirection and Program Termination |
the sys
module also has attributes for stdin, stdout, and stderr
>>> sys.stderr.write('Warning, log file not found starting a new one\n')
Warning, log file not found starting a new one
most direct way to terminate a script is to use sys.exit()
|
| String Pattern Matching |
the re
module provides regular expression tools for advanced string processing
>>> 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'when only simple capabilities are needed, string methods are preferred because they are easier to read and debug >>> 'tea for too'.replace('too', 'two')
'tea for two'
|
| Mathematics |
the math
module gives access to the underlying C library functions for floating-point math
>>> import math >>> math.cos(math.pi / 4) 0.70710678118654757 >>> math.log(1024, 2) 10.0the random module provides tools for making random selections >>> 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 from the interval [0.0, 1.0) 0.17970987693706186 >>> random.randrange(6) # random integer chosen from range(6) 4the statistics module calculates basic statistical properties (the mean, median, variance, etc.) of numeric data >>> import statistics >>> data = [2.75, 1.75, 1.25, 0.25, 0.5, 1.25, 3.5] >>> statistics.mean(data) 1.6071428571428572 >>> statistics.median(data) 1.25 >>> statistics.variance(data) 1.3720238095238095 |
| Internet Access |
a number of modules for accessing the internet and processing internet protocols
>>> from urllib.request import urlopen
>>> with urlopen('http://worldtimeapi.org/api/timezone/etc/UTC.txt') as response:
... for line in response:
... line = line.decode() # Convert bytes to a str
... if line.startswith('datetime'):
... print(line.rstrip()) # Remove trailing newline
datetime: 2022-01-01T01:36:47.689215+00:00
>>> 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()
|
| Dates and Times |
|
the datetime module
supplies classes for manipulating dates and times in both simple and complex ways while date and time arithmetic is supported, the focus of the implementation is on efficient member extraction for output formatting and manipulation the module also supports objects that are timezone aware >>> # dates are easily constructed and formatted
>>> from datetime import date
>>> now = date.today()
>>> now
datetime.date(2003, 12, 2)
>>> now.strftime("%m-%d-%y. %d %b %Y is a %A on the %d day of %B.")
'12-02-03. 02 Dec 2003 is a Tuesday on the 02 day of December.'
>>> # dates support calendar arithmetic
>>> birthday = date(1964, 7, 31)
>>> age = now - birthday
>>> age.days
14368
|
| Data Compression |
| common data archiving and compression formats are directly supported by modules including |
| Performance Measurement |
|
interest in knowing the relative performance of different approaches to the same problem the timeit module can be used to determine performance advantage timeit provides fine level of granularity >>> from timeit import Timer
>>> Timer('t=a; a=b; b=t', 'a=1; b=2').timeit()
0.57535828626024577
>>> Timer('a,b = b,a', 'a=1; b=2').timeit()
0.54962537085770791
the profile and
pstats modules
provide tools for identifying time critical sections in larger blocks of code
|
| Quality Control |
|
the doctest
module provides a tool for scanning a module and validating tests embedded in a program's docstrings. test construction is as simple as cutting-and-pasting a typical call along with its results into the docstring improves the documentation by providing the user with an example allows the doctest module to make sure the code remains true to the documentation 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
doctest.testmod() # automatically validate the embedded tests
The
unittest module
is not as effortless as the doctest moduleallows a more comprehensive set of tests to be maintained in a separate file import unittest
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() # Calling from the command line invokes all tests
|
| Batteries Included |
|