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 < end;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:
- 编写一个类文件
- 编写一个main方法
- 将之编译成字节代码
- 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 = 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()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.
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
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.
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.
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) / c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);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# 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)# 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 aspath = " 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()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! "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 + b
oChild = Child()
oChild.add( " str1 " )
print oChild.data
print oChild.plus( 2 , 3 )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.py
def add_func(a,b):
return a + b
# b.py
from a import add_func # Also can be : import a
print " 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.py
b.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 sys
print 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 sys
sys.path.append( ' D:\\download ' )
from parent.child.a import add_func
print sys.path
print " Import add_func from module a "print " Result of 1 plus 2 is: "print add_func( 1 , 2 )总结
你会发现这个教程相当的简单.许多Python特性在代码中以隐含方式提出,这些特性包括:Python不需要显式声明数据类型,关键字说明,字符串函数的解释等等.我认为一个熟练的程序员应该对这些概念相当了解,这样在你挤出宝贵的一小时阅读这篇短短的教程之后,你能够通过已有知识的迁移类比尽快熟悉Python,然后尽快能用它开始编程.
当然,1小时学会Python颇有哗众取宠之嫌.确切的说,编程语言包括语法和标准库.语法相当于武术招式,而标准库应用实践经验则类似于内功,需要长期锻炼.Python学习了Java的长处,提供了大量极方便易用的标准库供程序员"拿来主义".(这也是Python成功的原因),在开篇我们看到了Python如何调用Windows cmd的例子,以后我会尽量写上各标准库的用法和一些应用技巧,让大家真正掌握Python.
但不管怎样,至少你现在会用Python代替繁琐的批处理写程序了.希望那些真的能在一小时内读完本文并开始使用Python的程序员会喜欢这篇小文章,谢谢!
