79 lines
1.8 KiB
Python
79 lines
1.8 KiB
Python
# _*_ coding: utf-8 _*_
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"""
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python_context.py by xianhu
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"""
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import contextlib
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# 自定义打开文件操作
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class MyOpen(object):
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def __init__(self, file_name):
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"""初始化方法"""
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self.file_name = file_name
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self.file_handler = None
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return
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def __enter__(self):
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"""enter方法，返回file_handler"""
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print("enter:", self.file_name)
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self.file_handler = open(self.file_name, "r")
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return self.file_handler
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def __exit__(self, exc_type, exc_val, exc_tb):
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"""exit方法，关闭文件并返回True"""
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print("exit:", exc_type, exc_val, exc_tb)
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if self.file_handler:
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self.file_handler.close()
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return True
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# 使用实例
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with MyOpen("python_base.py") as file_in:
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for line in file_in:
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print(line)
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raise ZeroDivisionError
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# 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
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# 内置库contextlib的使用
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@contextlib.contextmanager
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def open_func(file_name):
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# __enter__方法
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print("open file:", file_name, "in __enter__")
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file_handler = open(file_name, "r")
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yield file_handler
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# __exit__方法
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print("close file:", file_name, "in __exit__")
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file_handler.close()
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return
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# 使用实例
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with open_func("python_base.py") as file_in:
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for line in file_in:
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print(line)
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break
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# 内置库contextlib的使用
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class MyOpen2(object):
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def __init__(self, file_name):
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"""初始化方法"""
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self.file_handler = open(file_name, "r")
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return
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def close(self):
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"""关闭文件，会被自动调用"""
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print("call close in MyOpen2")
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if self.file_handler:
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self.file_handler.close()
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return
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# 使用实例
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with contextlib.closing(MyOpen2("python_base.py")) as file_in:
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pass
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