> import os
> os.getcwd()   # 返回当前的工作目录
'C:\\Python34'
> os.chdir('/server/accesslogs')  # 修改当前的工作目录
> os.system('mkdir today')  # 执行系统命令 mkdir 
0

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

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

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

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

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

> 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'

> 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

> 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('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()  # 自动验证嵌入测试

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)
    self.assertRaises(ZeroDivisionError, average, [])
    self.assertRaises(TypeError, average, 20, 30, 70)

unittest.main() # Calling from the command line invokes all tests