Python 3.7.x 介绍-7 标准库

Posted 2022-11-28 Joey-Zhang

标准库介绍

操作系统接口

>>> import os
>>> os.getcwd()      # Return the current working directory
'C:\\\\Python37'
>>> os.chdir('/server/accesslogs')   # Change current working directory
>>> os.system('mkdir today')   # Run the command mkdir in the system shell

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

文件通配符

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

命令行参数

通用实用程序脚本通常需要处理命令行参数。这些参数作为列表存储在sys模块的argv属性中。

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

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

字符串模式匹配

re模块为高级字符串处理提供正则表达式工具

>>> 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'

数学

math模块提供对浮点数学的底层C库函数的访问

>>> 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)

>>> 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 访问

有许多模块可用于访问互联网和处理互联网协议。其中两个最简单的是用于从URL检索数据的urllib.request和用于发送邮件的smtplib：

>>> 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)

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

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

日期和时间

>>> # 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

数据压缩

模块直接支持通用数据存档和压缩格式，包括：zlib，gzip，bz2，lzma，zipfile和tarfile

>>> 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

性能评估

一些Python用户对了解同一问题的不同方法的相对性能产生了浓厚的兴趣。 Python提供了一种可以立即回答这些问题的测量工具。

>>> 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

质量控制

doctest模块提供了一个工具，用于扫描模块并验证程序文档字符串中嵌入的测试。 测试构造就像将典型调用及其结果剪切并粘贴到文档字符串一样简单。 这通过向用户提供示例来改进文档，并且它允许doctest模块确保代码保持对文档的真实性：

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

unittest模块不像doctest模块那样轻松，但它允许在单独的文件中维护更全面的测试集：

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