文件操作-with和上下文管理器

代码：

 # -*- coding:utf-8 -*-
 # 普通版 如果写入的过程中出错 则不会释放资源
 def m1():
     f = open("test.txt","w")
     f.write("hello python")
     f.close()
 # 进阶版
 def m2():
     f = open("test2.txt","w")
     try:
         f.write("hello python2")
     except IOError:
         print("oops error")
     finally:
         f.close()
 # 高级
 def m3():
     with open("test3.txt","w") as f:
         f.write("hello python3")
 m1()
 m2()
 m3()

 # 上下文管理器
 # 任何实现了 __enter__() 和 __exit__() 方法的对象都可称之为上下文管理器，上下文管理器对象可以使用 with 关键字。显然，文件（file）对象也实现了上下文管理器。
 class File(object):
     def __init__(self,filename,model):
         self.filename = filename
         self.model = model

     def __enter__(self):
         print("--enter--")
         self.f = open(self.filename,self.model)
         return self.f

     def __exit__(self, *args):
         print("--exit--")
         self.f.close()

 with File("test4.txt","w") as f:
     f.write("hello python4")   # 输出  --enter--
                                     # --exit - -
 # 装饰器实现上下文管理器
 from contextlib import contextmanager

 @contextmanager
 def my_open(path,model,encod):
     f = open(path,model,encoding=encod)
     yield f
     f.close()

 with my_open("test5.txt","w",'utf-8') as f:
     f.write("contextmanager实现上下文管理器")