# _*_ coding: utf-8 _*_ """ python_context.py by xianhu """ import contextlib # 自定义打开文件操作 class MyOpen(object): def __init__(self, file_name): """初始化方法""" self.file_name = file_name self.file_handler = None return def __enter__(self): """enter方法，返回file_handler""" 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): """exit方法，关闭文件并返回True""" print("exit:", exc_type, exc_val, exc_tb) if self.file_handler: self.file_handler.close() return True # 使用实例 with MyOpen("python_base.py") as file_in: for line in file_in: print(line) raise ZeroDivisionError # 代码块中主动引发一个除零异常，但整个程序不会引发异常 # 内置库contextlib的使用 @contextlib.contextmanager def open_func(file_name): # __enter__方法 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() return # 使用实例 with open_func("python_base.py") as file_in: for line in file_in: print(line) break # 内置库contextlib的使用 class MyOpen2(object): def __init__(self, file_name): """初始化方法""" self.file_handler = open(file_name, "r") return def close(self): """关闭文件，会被自动调用""" print("call close in MyOpen2") if self.file_handler: self.file_handler.close() return # 使用实例 with contextlib.closing(MyOpen2("python_base.py")) as file_in: pass