Summary of 12 basic knowledge commonly used in python programming

>>> line = ' 
>>> mo=re.compile(r'(?<=SRC=)"([\w+\.]+)"',re.I)  

>>> mo.sub(r'"\1****"',line)  
' 

>>> mo.sub(r'replace_str_\1',line)  
''< /span> 

>>> mo.sub(r'"testetstset"',line)  
'

import os
fileList = []
rootdir = "/data"
for root, subFolders, files in os.walk(rootdir):
if '.svn' in subFolders: subFolders.remove('.svn')  # 排除特定目录
for file in files:
  if file.find(".t2t") != -1:# 查找特定扩展名的文件
      file_dir_path = os.path.join(root,file)
      fileList.append(file_dir_path)  

print fileList

>>> a = [('2011-03-17', '2.26', 6429600, '0.0'), ('2011-03-16', '2.26', 12036900, '-3.0'),
 ('2011-03-15', '2.33', 15615500,'-19.1')]
>>> print a[0][0]
2011-03-17
>>> b = sorted(a, key=lambda result: result[1],reverse=True)
>>> print b
[('2011-03-15', '2.33', 15615500, '-19.1'), ('2011-03-17', '2.26', 6429600, '0.0'),
('2011-03-16', '2.26', 12036900, '-3.0')]
>>> c = sorted(a, key=lambda result: result[2],reverse=True)
>>> print c
[('2011-03-15', '2.33', 15615500, '-19.1'), ('2011-03-16', '2.26', 12036900, '-3.0'),
('2011-03-17', '2.26', 6429600, '0.0')]

>>> lst= [(1,'sss'),(2,'fsdf'),(1,'sss'),(3,'fd')]
>>> set(lst)
set([(2, 'fsdf'), (3, 'fd'), (1, 'sss')])
>>>
>>> lst = [1, 1, 3, 4, 4, 5, 6, 7, 6]
>>> set(lst)
set([1, 3, 4, 5, 6, 7])

>>> from operator import itemgetter
>>> aa = {"a":"1","sss":"2","ffdf":'5',"ffff2":'3'}
>>> sort_aa = sorted(aa.items(),key=itemgetter(1))
>>> sort_aa
[('a', '1'), ('sss', '2'), ('ffff2', '3'), ('ffdf', '5')]

>>> params = {"server":"mpilgrim", "database":"master", "uid":"sa", "pwd":"secret"}
>>> ["%s=%s" % (k, v) for k, v in params.items()]
['server=mpilgrim', 'uid=sa', 'database=master', 'pwd=secret']
>>> ";".join(["%s=%s" % (k, v) for k, v in params.items()])
'server=mpilgrim;uid=sa;database=master;pwd=secret'

>>> a = 'server=mpilgrim;uid=sa;database=master;pwd=secret'
>>> aa = {}
>>> for i in a.split(';'):aa[i.split('=',1)[0]] = i.split('=',1)[1]
...
>>> aa
{'pwd': 'secret', 'database': 'master', 'uid': 'sa', 'server': 'mpilgrim'}

将时间对象转换成字符串
>>> import datetime
>>> datetime.datetime.now().strftime("%Y-%m-%d %H:%M")
  '2011-01-20 14:05' 

时间大小比较
>>> import time
>>> t1 = time.strptime('2011-01-20 14:05',"%Y-%m-%d %H:%M")
>>> t2 = time.strptime('2011-01-20 16:05',"%Y-%m-%d %H:%M")
>>> t1 > t2
  False
>>> t1 < t2
  True 

时间差值计算,计算8小时前的时间
>>> datetime.datetime.now().strftime("%Y-%m-%d %H:%M")
  '2011-01-20 15:02'
>>> (datetime.datetime.now() - datetime.timedelta(hours=8)).strftime("%Y-%m-%d %H:%M")
  '2011-01-20 07:03' 

将字符串转换成时间对象
>>> endtime=datetime.datetime.strptime('20100701',"%Y%m%d")
>>> type(endtime)
  
>>> print endtime
  2010-07-01 00:00:00 

将从 1970-01-01 00:00:00 UTC 到现在的秒数，格式化输出   

>>> import time
>>> a = 1302153828
>>> time.strftime("%Y-%m-%d %H:%M:%S",time.localtime(a))
  '2011-04-07 13:23:48'

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys,os,getopt
def usage():
print '''''
Usage: analyse_stock.py [options...]
Options:
-e : Exchange Name
-c : User-Defined Category Name
-f : Read stock info from file and save to db
-d : delete from db by stock code
-n : stock name
-s : stock code
-h : this help info
test.py -s haha -n "HA Ha"
''' 

try:
opts, args = getopt.getopt(sys.argv[1:],'he:c:f:d:n:s:')
except getopt.GetoptError:
usage()
sys.exit()
if len(opts) == 0:
usage()
sys.exit()  

for opt, arg in opts:
if opt in ('-h', '--help'):
  usage()
  sys.exit()
elif opt == '-d':
  print "del stock %s" % arg
elif opt == '-f':
  print "read file %s" % arg
elif opt == '-c':
  print "user-defined %s " % arg
elif opt == '-e':
  print "Exchange Name %s" % arg
elif opt == '-s':
  print "Stock code %s" % arg
elif opt == '-n':
  print "Stock name %s" % arg  

sys.exit()

截取字符串输出,下面例子将只输出字符串的前3个字母
>>> str="abcdefg"
>>> print "%.3s" % str
  abc
按固定宽度输出，不足使用空格补全,下面例子输出宽度为10
>>> str="abcdefg"
>>> print "%10s" % str
     abcdefg
截取字符串，按照固定宽度输出
>>> str="abcdefg"
>>> print "%10.3s" % str
         abc
浮点类型数据位数保留
>>> import fpformat
>>> a= 0.0030000000005
>>> b=fpformat.fix(a,6)
>>> print b
  0.003000
对浮点数四舍五入,主要使用到round函数
>>> from decimal import *
>>> a ="2.26"
>>> b ="2.29"
>>> c = Decimal(a) - Decimal(b)
>>> print c
  -0.03
>>> c / Decimal(a) * 100
  Decimal('-1.327433628318584070796460177')
>>> Decimal(str(round(c / Decimal(a) * 100, 2)))
  Decimal('-1.33')

>>> num = 10
>>> print "Hex = %x,Dec = %d,Oct = %o" %(num,num,num)
  Hex = a,Dec = 10,Oct = 12

使用 os.system() 调用系统命令 , 程序中无法获得到输出和返回值
>>> import os
>>> os.system('ls -l /proc/cpuinfo')
>>> os.system("ls -l /proc/cpuinfo")
  -r--r--r-- 1 root root 0  3月 29 16:53 /proc/cpuinfo
  0 

使用 os.popen() 调用系统命令, 程序中可以获得命令输出，但是不能得到执行的返回值
>>> out = os.popen("ls -l /proc/cpuinfo")
>>> print out.read()
  -r--r--r-- 1 root root 0  3月 29 16:59 /proc/cpuinfo  

使用 commands.getstatusoutput() 调用系统命令, 程序中可以获得命令输出和执行的返回值
>>> import commands
>>> commands.getstatusoutput('ls /bin/ls')
  (0, '/bin/ls')

try:
    do_some_func()
except KeyboardInterrupt:
    print "User Press Ctrl+C,Exit"
except EOFError:
    print "User Press Ctrl+D,Exit"

一次性读入文件到列表，速度较快，适用文件比较小的情况下
track_file = "track_stock.conf"
fd = open(track_file)
content_list = fd.readlines()
fd.close()
for line in content_list:
    print line  

逐行读入，速度较慢,适用没有足够内存读取整个文件(文件太大)
fd = open(file_path)
fd.seek(0)
title = fd.readline()
keyword = fd.readline()
uuid = fd.readline()
fd.close()  

写文件 write 与 writelines 的区别   

Fd.write(str) : 把str写到文件中，write()并不会在str后加上一个换行符
Fd.writelines(content) : 把content的内容全部写到文件中,原样写入，不会在每行后面加上任何东西