python基础-python上下文管理协议:with语句
with 语句
# with open('a.txt') as f: # '代码块' # 上述叫做上下文管理协议,即with语句,为了让一个对象兼容with语句, # 必须在这个对象的类中声明__enter__和__exit__方法 class Open: def __init__(self,name): self.name=name def __enter__(self): print('出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量,即f') # return self def __exit__(self, exc_type, exc_val, exc_tb): print('当with中代码块执行完毕时执行我') with Open('a.txt') as f: print('=====>执行代码块') # print(f,f.name) # 运行结果: # 出现with语句,对象的__enter__被触发,有返回值则赋值给as声明的变量,即f # =====>执行代码块 # 当with中代码块执行完毕时执行我