老程序员通过一篇文章快速学会python这门新语言

老程序员快速掌握一门新的语言，如果还是逐个看语法手册，太费时间了，通过一篇文章，无需太多解析，自己就可以看个大概了。接下来看看标准库，然后就可以开始干活了。先来看一个简单的任务：简单测试局域网中的电脑是否连通.这些电脑的ip范围从192.168.0.101到192.168.0.200.   import subprocesscmd="cmd.exe"begin=101end=200while begin<end:    p=subprocess.Popen(cmd,shell=True,stdout=subprocess.PIPE,                   stdin=subprocess.PIPE,                   stderr=subprocess.PIPE)    p.stdin.write("ping 192.168.1."+str(begin)+"\n")    p.stdin.close()    p.wait()    print "execution result: %s"%p.stdout.read()这个程序保存之后可以直接运行.2 快速入门2.1 Hello world    安装完Python之后,打开IDLE(Python GUI) , 该程序是Python语言解释器,你写的语句能够立即运行.我们写下一句著名的程序语句:print "Hello,world!"    并按回车.你就能看到这句被K&R引入到程序世界的名言.    在解释器中选择"File"--"New Window" 或快捷键 Ctrl+N , 打开一个新的编辑器.写下如下语句:print "Hello,world!"raw_input("Press enter key to close this window");    保存为a.py文件.按F5,你就可以看到程序的运行结果了.这是Python的第二种运行方式.    找到你保存的a.py文件,双击.也可以看到程序结果.Python的程序能够直接运行.2.2 国际化支持    我们换一种方式来问候世界.新建一个编辑器并写如下代码:print "欢迎来到奥运中国!"raw_input("Press enter key to close this window");    在你保存代码的时候,Python会提示你是否改变文件的字符集,结果如下:# -*- coding: cp936 -*- print "欢迎来到奥运中国!"raw_input("Press enter key to close this window");    将该字符集改为我们更熟悉的形式:# -*- coding: GBK -*- print "欢迎来到奥运中国!" # 使用中文的例子raw_input("Press enter key to close this window");    程序一样运行良好.2.3 方便易用的计算器    用微软附带的计算器来计数实在太麻烦了.打开Python解释器,直接进行计算:a=100.0b=201.1c=2343print (a+b+c)/c2.4 字符串,ASCII和UNICODE    可以如下打印出预定义输出格式的字符串:print """Usage: thingy [OPTIONS]     -h                        Display this usage message     -H hostname               Hostname to connect to"""    字符串是怎么访问的?请看这个例子:word="abcdefg"a=word[2]print "a is: "+ab=word[1:3]print "b is: "+b # index 1 and 2 elements of word.c=word[:2]print "c is: "+c # index 0 and 1 elements of word.d=word[0:]print "d is: "+d # All elements of word.e=word[:2]+word[2:]print "e is: "+e # All elements of word.f=word[-1]print "f is: "+f # The last elements of word.g=word[-4:-2]print "g is: "+g # index 3 and 4 elements of word.h=word[-2:]print "h is: "+h # The last two elements.i=word[:-2]print "i is: "+i # Everything except the last two charactersl=len(word)print "Length of word is: "+ str(l)    请注意ASCII和UNICODE字符串的区别:print "Input your Chinese name:"s=raw_input("Press enter to be continued");print "Your name is  : " +s;l=len(s)print "Length of your Chinese name in asc codes is:"+str(l);a=unicode(s,"GBK")l=len(a)print "I'm sorry we should use unicode char!Characters number of your Chinese \name in unicode is:"+str(l);2.5 使用List    类似Java里的List,这是一种方便易用的数据类型:word=['a','b','c','d','e','f','g']a=word[2]print "a is: "+ab=word[1:3]print "b is: "print b # index 1 and 2 elements of word.c=word[:2]print "c is: "print c # index 0 and 1 elements of word.d=word[0:]print "d is: "print d # All elements of word.e=word[:2]+word[2:]print "e is: "print e # All elements of word.f=word[-1]print "f is: "print f # The last elements of word.g=word[-4:-2]print "g is: "print g # index 3 and 4 elements of word.h=word[-2:]print "h is: "print h # The last two elements.i=word[:-2]print "i is: "print i # Everything except the last two charactersl=len(word)print "Length of word is: "+ str(l)print "Adds new element"word.append('h')print word2.6 条件和循环语句# Multi-way decisionx=int(raw_input("Please enter an integer:"))if x<0:    x=0    print "Negative changed to zero"elif x==0:    print "Zero"else:    print "More"# Loops Lista = ['cat', 'window', 'defenestrate']for x in a:    print x, len(x)2.7 如何定义函数# Define and invoke function.def sum(a,b):    return a+bfunc = sumr = func(5,6)print r# Defines function with default argumentdef add(a,b=2):    return a+br=add(1)print rr=add(1,5)print r    并且,介绍一个方便好用的函数:# The range() functiona =range(5,10)print aa = range(-2,-7)print aa = range(-7,-2)print aa = range(-2,-11,-3) # The 3rd parameter stands for stepprint a2.8 文件I/Ospath="D:/download/baa.txt"f=open(spath,"w") # Opens file for writing.Creates this file doesn't exist.f.write("First line 1.\n")f.writelines("First line 2.")f.close()f=open(spath,"r") # Opens file for readingfor line in f:    print linef.close()2.9 异常处理s=raw_input("Input your age:")if s =="":    raise Exception("Input must no be empty.")try:    i=int(s)except ValueError:    print "Could not convert data to an integer."except:    print "Unknown exception!"else: # It is useful for code that must be executed if the try clause does not raise an exception    print "You are %d" % i," years old"finally: # Clean up action    print "Goodbye!"2.10 类和继承class Base:    def __init__(self):        self.data = []    def add(self, x):        self.data.append(x)    def addtwice(self, x):        self.add(x)        self.add(x)# Child extends Baseclass Child(Base):    def plus(self,a,b):        return a+boChild =Child()oChild.add("str1")print oChild.dataprint oChild.plus(2,3)2.11 包机制    每一个.py文件称为一个module,module之间可以互相导入.请参看以下例子:# a.pydef add_func(a,b):    return a+b# b.pyfrom a import add_func # Also can be : import aprint "Import add_func from module a"print "Result of 1 plus 2 is: "print add_func(1,2)    # If using "import a" , then here should be "a.add_func"    module可以定义在包里面.Python定义包的方式稍微有点古怪,假设我们有一个parent文件夹,该文件夹有一个child子文件夹.child中有一个module a.py . 如何让Python知道这个文件层次结构?很简单,每个目录都放一个名为_init_.py 的文件.该文件内容可以为空.这个层次结构如下所示: parent   --__init_.py  --child    -- __init_.py    --a.pyb.py    那么Python如何找到我们定义的module?在标准包sys中,path属性记录了Python的包路径.你可以将之打印出来:import sysprint sys.path    通常我们可以将module的包路径放到环境变量PYTHONPATH中,该环境变量会自动添加到sys.path属性.另一种方便的方法是编程中直接指定我们的module路径到sys.path 中:import syssys.path.append('D:\\download')from parent.child.a import add_funcprint sys.pathprint "Import add_func from module a"print "Result of 1 plus 2 is: "print add_func(1,2)