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# _*_ 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