# _*_ 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