上下文管理器

Class Methods

1.创建Open类

class Open:
    def __init__(self,file_name):
        self.file_name = file_name
        self.file_handler = None
        return

    def __enter__(self):
        print("enter",self.file_name)
        self.file_handler = open(self.file_name,'r')
        return self.file_handler

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("exit",exc_type,exc_val,exc_tb)
        if self.file_handler:
            self.file_handler.close()
        return True

2.调用实例

# 使用实例
with Open("python_base.py") as file_in:
    for line in file_in:
        print(line)
        raise ZeroDivisionError   #抛出一个异常

进入with语句会先调用init与enter函数初始化与创建文件
当执行完with语句后会调用exit函数处理异常，防止异常向上传递

Contextlib库

1.使用装饰器@contextlib.contextmanager将函数转化为上下文管理器

@contextlib.contextmanager
def open_func(file_name):
    print("open file:",file_name,"in __enter__")
    file_handler = open(file_name,'r')

    yield file_handler

#exit方法
    print("close file:",file_name,"in__exit__")
    file_handler.close()

2.使用实例

with open_func("test.txt") as file_in:
    for line in file_in:
        print(line)
        break

Class and Contextlib

1.创建Open类

class Open():
    def __init__(self,file_name):
        self.file_name = file_name
        self.file_handler = open(file_name,"r")

    def close(self):
        print("close file Open")
        if self.file_handler:
            self.file_handler.close()

2.使用实例

with contextlib.closing(Open("text.txt")) as file_in: