卖萌的弱渣

I am stupid, I am hungry.

Python: Standard Library

Operating System Interface

The os module provides dozens of functions to interact wieh OS.

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>>> import os
>>> os.getcwd()                     # Return current working directory
'C:\\Python35'
>>> os.chdir('/server/accesslogs')  # Change current working directory
>>> os.system('mkdir today')        # Run the command "mkdir" in system shell
0

Be usre to use import os rather than from os import *

  • The built-in dir() and help() functions are useful.
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>>> dir(os)   # return all module functions
>>> help(os)  # return manual page.
  • The shutil can provide higher level interface
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>>> shutil.copyfile('data.db', 'archive.db')
'archive.db'

>>> shutil.move('/build/executables', 'installdir')
'installdir'

File Wildcards

glob module provides a function for making file list from directorywildcard searches

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

Command Line Arguments

sys module can process command line arguments. If you run python demo.py one two three and demo.py looks like

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

Error Output Redirection and Program Termination

sys module has attributes for stdin, stdout, and stderr

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

String Pattern Matching

re module provides regular expression tools for string processing.

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>>> 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 simple capabilities are needed, string methods are preferred

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

Mathematics

  • math module gives access to C library functions for loating point math.
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>>> import math
>>> math.cos(math.pi / 4)
0.707106

>>> math.log(1024, 2)
10.0
  • random module provides tools for making random selections.
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>>> import random
>>> random.choice(['apple', 'pear', 'banana'])
'apple'

>>> random.sample(range(100), 10)    # find 10 sampling without replacement
[30, 83, 16,4,8,81,41,50,18,33]

>>> random.random()  # random float
0.17970987

>>> random.randrange(6) # random integer chosen from range(6)
4
  • statistics module calculates basic statistical properties of numeric data
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>>> import statistics
>>> data = [2.7, 1.75, 1.25, 0.25, 0.5 1.25, 3.5]
>>> statistics.mean(data)
1.6071

>>> statistics.median(data)
1.25

>>> statistics.variance(data)
1.372023

Internet Access

urllib.request can retrieve data from URLs and smtplib can send mails.

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>>> 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')
            if 'EST' in line or 'EDT' in line:   # look for eastern time
                print(line)

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

If there is a mailserver running on localhost

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server = smtplib.SMTP('localhost')
server.sendmail('a@example.org', 'b@example.org',
"""
This is mail content.
To: b@example.org
From: a@example.org
""")
server.quit()

Dates and Times

datatime module supports dates, times and time zone

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>>> from datetime import date
>>> now = date.today()
>>> now
datetime.date(2003, 12, 2)
>>> now.strftime("%m-%d0%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

>>> birth = date(1964, 7, 31)
>>> age = now - birthday
>>> age.days
14368

Data Compression

Use module zlib, gzip, bz2, lzma, zipfile and tarfile archive and compress data.

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>>> 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

Performance Measurement

timeit can quickly demonstrate a modest performance advantage

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>>> from timeit import Timer
>>> Timer('t=a;a=b;b=t','a=1;b=2').timeit()    # Test code 1
0.5753

>>> Timer('a,b=b,a', 'a=1; b=2').timeit()      # Test code 2
0.5496

Compared with timeit moduel which can test in fine level of granularity, profile and pstats can test large block of codes