Python入门教程 超详细1小时学会Python
为什么使用Python
假设我们有这么一项任务: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. 思路:用shell编程.(Linux通常是bash而Windows是批处理脚本).例如,在Windows上用ping ip 的命令依次测试各个机器并得到控制台输出.由于ping通的时候控制台文本通常是"Reply from ... " 而不通的时候文本是"time out ... " ,所以,在结果中进行字符串查找,即可知道该机器是否连通.
实现:Java代码如下:
String cmd="cmd.exe ping ";
String ipprefix="192.168.10.";
int begin=101;
int end=200;
Process p=null;
for(int i=begin;i p= Runtime.getRuntime().exec(cmd+i); String line = null; BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream())); while((line = reader.readLine()) != null) { //Handling line , may logs it. } reader.close(); p.destroy(); } 这段代码运行得很好,问题是为了运行这段代码,你还需要做一些额外的工作.这些额外的工作包括: 1. 编写一个类文件 2. 编写一个main方法 3. 将之编译成字节代码 4. 由于字节代码不能直接运行,你需要再写个小小的bat或者bash脚本来运行. 当然,用C/C++同样能完成这项工作.但C/C++不是跨平台语言.在这个足够简单的例子中也许看不出C/C++和Java实现的区别,但在一些更为复杂的场景,比如要将连通与否的信息记录到网络数据库.由于Linux和Windows的网络接口实现方式不同,你不得不写两个函数的版本.用Java就没有这样的顾虑. 同样的工作用Python实现如下: import subprocess cmd="cmd.exe" begin=101 end=200 while begin 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() 对比Java,Python的实现更为简洁,你编写的时间更快.你不需要写main函数,并且这个程序保存之后可以直接运行.另外,和Java一样,Python也是跨平台的. 有经验的C/Java程序员可能会争论说用C/Java写会比Python写得快.这个观点见仁见智.我的想法是当你同时掌握Java和Python之后,你会发现用Python写这类程序的速度会比Java快上许多.例如操作本地文件时你仅需要一行代码而不需要Java的许多流包装类.各种语言有其天然的适合的应用范围.用Python处理一些简短程序类似与操作系统的交互编程工作最省时省力. ________________________________________ Python应用场合 足够简单的任务,例如一些shell编程.如果你喜欢用Python设计大型商业网站或者设计复杂的游戏,悉听尊便. ________________________________________ 2 快速入门 2.1 Hello world 安装完Python之后(我本机的版本是2.5.4),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,对比Java,这是一个优势. ________________________________________ 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=100.0 b=201.1 c=2343 print (a+b+c)/c ________________________________________ 2.4 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: "+a b=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 characters l=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: "+a b=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 characters l=len(word) print "Length of word is: "+ str(l) print "Adds new element " word.append('h') print word ________________________________________ 2.6 条件和循环语句 # Multi-way decision x=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 List a = ['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+b func = sum r = func(5,6) print r # Defines function with default argument def add(a,b=2): return a+b r=add(1) print r r=add(1,5) print r 并且,介绍一个方便好用的函数: # The range() function a =range(5,10) print a a = range(-2,-7) print a a = range(-7,-2) print a a = range(-2,-11,-3) # The 3rd parameter stands for step print a ________________________________________ 2.8 文件I/O spath="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 reading for line in f: print line f.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: