内置open（）函数对外部文件的操作

 >>> file=open('c://333.csv','r')  一些基本打开关闭操作
 >>> s=file.read()
 >>> print s
 ,add,age,name
 0,beijing,12,zhang
 1,shanghai,24,li
 2,tainjing,25,wang
 >>> file.close()

 >>> file=open('c://333.csv','r')
 >>> file2=open('c://111.csv','w')   将333内容写到111中
 >>> file2.write(file.read())
 >>> file2.close()
 >>> file.close()
 >>> file2=open('c://111.csv')
 >>> file2=open('c://111.csv','r')
 >>> s=file2.read()
 >>> print s
 ,add,age,name
 0,beijing,12,zhang
 1,shanghai,24,li
 2,tainjing,25,wang