简明python教程学习笔记(三)

Python一个备份程序

这里需要调用rar命令，首先把rar命令加入到环境变量里面来：

我的RAR.exe 在C:\Program Files\WinRAR，加入环境变量后，示例备份程序helloworld.py mymodule.py到myPythonProgram.rar

<span style="font-family:Microsoft YaHei;font-size:14px;">#Backup script#DOS下解压命令行：rar a myPythonProgram mymodule.py helloworld.py#导入模块import os  import time#源路径source = [r'.\mymodule.py', r'.\helloworld.py']#目标路径targetDir = r'.\myPythonProgram'#DOS压缩命令rarCommand = 'rar a %s %s' % (targetDir, ' '.join(source))#执行DOS命令if os.system(rarCommand) == 0:    print('Backup successful')else:    print('failed')    print(rarCommand)</span>

Python面向对象一个程序示例

一个例子代码展示如下：

<span style="font-family:Microsoft YaHei;font-size:14px;">#using class and object#定义类class Person:    #类变量population,相当于c++中静态成员变量    population = 0    #init初始化函数 相当于c++构造函数    def __init__(self, name):        #self.name是对象成员        self.name = name        print('initialise %s' % self.name)               Person.population += 1    #del函数 相当于c++析构函数    def __del__(self):        print('%s is dying' % self.name)       if self.__class__.population > 0:             self.__class__.population -= 1    #成员函数    def sayHi(self):        print('hi, my name is %s' % self.name)    #成员函数    def howMany(self):        if Person.population == 1:            print('I am the last person')        else:            print('there are %d person left' % Person.population)#创造对象p1 = Person('Tom')p1.sayHi()p1.howMany()p2 = Person('Jack')p2.sayHi()p2.howMany()#result: # initialise Tom# hi, my name is Tom# I am the last person# initialise Jack# hi, my name is Jack# there are 2 person left# Jack is dying# Tom is dying</span>

这里需要注意在类的del函数里面，访问类变量(class variable)用self.__class__.来代替，否则可能会报如下错误：

Exception AttributeError: "'NoneType' object has no attribute

python读写文件示例

一个读写文件的示例：

<span style="font-family:Microsoft YaHei;font-size:14px;">#using files#待写入的文本text = '''\I felt very happy.Today I go outHe is stupid'''#以写入方式打开文件f = open('test.txt', 'w') #可以是二进制写'wb'#写入f.write(text)#关闭文件f.close()#读文件f = open('test.txt', 'r') #不写‘r’，默认是只读打开,也可以二进制读'rb'while True:    line = f.readline()    if len(line) == 0: #为0表示文件结束                break    else:        print(line)#关闭文件    f.close()#result:# I felt very happy.# Today I go out# He is stupidV</span>

python自定义异常对象、捕获异常

<span style="font-family:Microsoft YaHei;font-size:14px;">#using exception#处理异常try:    text = input('please input something:')except EOFError:    print('you enter EOF!')except KeyboardInterrupt:    print('you canceld the operation')else:    print('you entered %s' % text)#在windows DOS下结果：# please input something:^Z# you enter EOF!# please input something:you canceld the operation [ctr + c]# please input something:how are you# you entered how are you#自定义异常对象并引发class MyInputException(Exception):      def __init__(self, length, least):          Exception.__init__(self)          self.length = length          self.least = least  try:    text = input('please input again:')    if len(text) < 4:        raise MyInputException(len(text), 4)except EOFError:    print('you input EOF!')except MyInputException as ex:    print('you enter %d , at least %d' % (ex.length, ex.least)) finally:    print('you entered %s' % text)</span>

sys.argv小程序

下面这个例子来自a byte of python是练习sys.argv的

<span style="font-family:Microsoft YaHei;font-size:14px;">#using sys.argvimport sys#读文件函数def readfiles(filename):    try:        f = open(filename, 'r')    except Exception:        print('%s not exist!' % filename)        return    while True:        line = f.readline()        if len(line) == 0:            break        else:            print(line)#命令行命令解析if sys.argv[1].startswith('--'):  #解析参数选项    option = sys.argv[1][2:]    if option == 'version':        print('version 1.1')    elif option == 'help':        print('''\    This program prints file to standard    option includes:    --version: print current version    --help: show help''')    else:        print('unknown option')else:                             #打印文件    for filename in sys.argv[1:]:  #注意这里元组slice的用法 灵活方便</span>