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python_context.py
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78 lines (60 loc) · 1.82 KB
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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