fromcontextlib import contextmanager # 定义上下文管理器函数 @contextmanager def function_based_context_manager():print("进入上下文: __enter__")yield"这是个基于上下文管理器的函数"print("离开上下文: __exit__")# with语句中使用上下文管理器函数 with function_based_context_manager()asyield_text:print...
opened_file.undefined_function()#Output: Exception has been handled 我们的__exit__方法返回了True,因此没有异常会被with语句抛出。 这还不是实现上下文管理器的唯一方式。还有一种方式,我们会在下一节中一起看看。 基于生成器的实现 我们还可以用装饰器(decorators)和生成器(generators)来实现上下文管理器。 P...
Thecontextlib module of the standard Python library contains a decorator calledcontextmanager.This decorator can be used on a generator function to create a factory of context managers. Let us see how this works. We have defined a function; it contains theyield keyword, which makes it a genera...
# currently bypasses the instance docstring and shows the docstring #fortheclassinstead.# See http://bugs.python.org/issue19404formore details.def_recreate_cm(self):# _GCM instances are one-shot context managers,so the #CMmust be recreated each time a decoratedfunctionis # calledreturnself.__...
Python'scontextlibmodule includes adecoratorwhich allows for creating context managers using a function syntax (instead of using the typical class syntax we saw above): fromcontextlibimportcontextmanagerimportos@contextmanagerdefset_env_var(var_name,new_value):original_value=os.environ.get(var_name)...
import functoolsdef my_decorator(func): @functools.wraps(func) def wrapper(*args, **kwargs): print("Before the function call") result = func(*args, **kwargs) print("After the function call") return result return wrapper@my_decoratordef say_hello(name): print(f"...
无需手动关闭文件 # 使用例子 example_function('file1.txt', 'file2.txt')4.「contextlib....
('Doing work in the wrapped function')# output# __init__(as decorator)## __init__(as context manager)# __enter__(as context manager)# Doing work in the context# __exit__(as context manager)## __enter__(as decorator)# Doing work in the wrapped function# __exit__(as decorator...
L-Local(function):函数内的名字空间 E-Enclosing function locals:外部嵌套函数的名字空间(例如closure) G-Global(module):函数定义所在模块(文件)的名字空间 B-Builtin(Python):Python内置模块的名字空间 Python的命名空间是一个字典,字典内保存了变量名称与对象之间的映射关系,因此,查找变量名就是在命名空间字典中...
27.3. Implementing a Context Manager as a Generator¶ We can also implement Context Managers using decorators and generators. Python has a contextlib module for this very purpose. Instead of a class, we can implement a Context Manager using a generator function. Let’s see a basic, useless ...