Python 基本笔记

1.语法  : 冒号的使用

>>> pystr = "Python"
>>> pystr[0]	#输出 'P'
>>> pystr[2:5]	#输出 'tho' 即[2,5) (2<=下标值<5)
>>> pystr[-2]	#输出 'o'
>>> pystr[3:]	#输出 'hon' 即下标3开始到结束
>>> pystr[:2]	#输出 'Py'  即[0,2)下标0开始到1结束
>>> pystr[::-1]	#可以当做"翻转"操作
'nohtyP'
>>> pystr[::2]	#隔一个取一个
'Pto'

2.循环 for in

>>> aDict = {'host':'earth'}
>>> aDict['host']
'earth'
>>> aDict['port'] = 80		#新增一个数据
>>> aDict.keys()
['host', 'port']
>>> for key in aDict :
	print key,aDict[key]

host earth
port 80

3.列表解析
---可以在一行中使用for循环将所有的值放到一个列表中:

>>> squared = [x ** 2 for x in range(4)]
>>> squared

[0, 1, 4, 9]
4.进制转换函数
hex(num) 将数字转换成十六进制数并以字符串形式返回
oct(num) 将数字转换成八进制数并以字符串形式返回

5.ASCII 转换函数

>>> ord('a')
97
>>> chr(97)
'a'

6.Template的使用 substitute严谨 safe_substitute()不严谨会原样输出

>>> from string import Template
>>> s = Template('There are ${howmany} ${lang} Quotation Symbols')
>>> print s.substitute(lang='Python',howmany=3)
There are 3 Python Quotation Symbols

7.函数装饰器(方便操作日志等)

from time import ctime,sleep
def tsfunc(func):
	def wrappedFunc():
		print '[%s] %s() called' % (ctime(),func.__name__)
		return func()
	return wrappedFunc

@tsfunc
def foo():
	pass

foo()
sleep(4)

for i in range(2):
	sleep(1)
	foo()

输出结果
---------- python ----------
[Thu Dec 17 15:44:46 2009] foo() called
[Thu Dec 17 15:44:51 2009] foo() called
[Thu Dec 17 15:44:52 2009] foo() called
---------------------------------------------------
小例子

'writeOrRead.py'
import os
ls = os.linesep
print "Enter file name: \n"
fname = raw_input('>')
isOk = False
# get filename
while True:
    if os.path.exists(fname):
        print "read "+ fname
        print '-----------------------'
        break
    else:
        isOk = True
        break
if(isOk):
    # get file content(text) lines
    all = []
    print "\nEnter lines('.' by itself to quit).\n"
    print "write content:"
    # loop until user terminates input
    while True:
        entry = raw_input('>')
        if entry == '.':
            break
        else:
            all.append(entry)
    # write lines to file with proper line-ending
    fobj = open(fname,'w')
    fobj.writelines(['%s%s' % (x,ls) for x in all])
    fobj.close()
    print 'DONE!'
else:
    # read and display text file
    try:
        fobj = open(fname,'r')
    except IOError,e:
        print fname+" file open error:",e
    else:
        #display contents to the screen
        for eachLine in fobj:
            print eachLine,
        fobj.close()