python_context.py

# _*_ coding: utf-8 _*_

"""
python_context.py by wangxin

概念详解移步：
http://www.cnblogs.com/chenny7/p/4213447.html
"""

import contextlib


# 自定义打开文件操作
class MyOpen(object):

    def __init__(self, file_name):
        """初始化方法"""
        print("call __init__ in MyOpen")
        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)
        # 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
        raise ZeroDivisionError



# # 【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"""
#         print("call __init__ in MyOpen2")
#         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