10. Brief Tour of the Standard Library

10. 标准库简介

10.1. Operating System Interface

10.1. 操作系统接口

   >>> import os 
   >>> os.getcwd()      # Return the current working directory 
   'C:\\Python39' 
   >>> os.chdir('/server/accesslogs')   # Change current working directory 
   >>> os.system('mkdir today')   # Run the command mkdir in the system shell 
   0 
 

   >>> import os 
   >>> dir(os) 
    
   >>> help(os) 
    
 

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

10.2. File Wildcards

10.2. 文件通配符

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

10.3. Command Line Arguments

10.3. 命令行参数

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

   >>> import argparse 
   >>> from getpass import getuser 
   >>> parser = argparse.ArgumentParser(description='An argparse example.') 
   >>> parser.add_argument('name', nargs='?', default=getuser(), help='The name of someone to greet.') 
   >>> parser.add_argument('--verbose', '-v', action='count') 
   >>> args = parser.parse_args() 
   >>> greeting = ["Hi", "Hello", "Greetings! its very nice to meet you"][args.verbose % 3] 
   >>> print(f'{greeting}, {args.name}') 
   >>> if not args.verbose: 
   >>>     print('Try running this again with multiple "-v" flags!') 
 
 

10.4. Error Output Redirection and Program Termination

10.4. 错误输出重定向和程序终止

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

10.5. String Pattern Matching

10.5. 字符串模式匹配

   >>> 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' 
 

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

10.6. Mathematics

10.6. 数学

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

   >>> 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 
 

   >>> 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 
 

   >>> from urllib.request import urlopen 
   >>> with urlopen('http://tycho.usno.navy.mil/cgi-bin/timer.pl') as response: 
   ...     for line in response: 
   ...         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) 
 
   
Nov. 25, 09:43:32 PM EST 
 
   >>> 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() 
 

   >>> # 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 
 
 

   >>> import zlib 
   >>> s = b'witch which has which witches wrist watch' 
   >>> len(s) 
   41 
   >>> t = zlib.compress(s) 
   >>> len(t) 
   37 
   >>> zlib.decompress(t) 
   b'witch which has which witches wrist watch' 
   >>> zlib.crc32(s) 
   226805979 
 
 

   >>> 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 
 

   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 
 

   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