我可以防止在Python中修改对象吗？

Question

我想控制全局变量（或全局范围的变量），使其在程序初始化代码中仅设置一次，然后将其锁定。

我对全局变量使用UPPER_CASE_VARIABLES，但是我想有一种确定的方法，无论如何不要更改变量。

• python是否提供（或类似）功能？
• 您如何控制全局范围的html" target="_blank">变量？

Answer 1

Activestate有一个由古老的Alex
Martelli
撰写的题为“ Constants in
Python
”的食谱
，

用于创建具有创建后无法反弹的属性的模块。听起来像您在寻找什么，除了大写字母-
但这可以通过检查属性名称是否全部大写来添加。const

当然，这可以由有决心的人规避，但这就是Python的方式—并被大多数人视为“好事”。但是，要使其变得更困难一点，我建议您不要去添加所谓的显而易见的__delattr__方法，因为人们可以随后删除名称，然后将其重新添加回不同的值。

这就是我要采取的措施：

# Put in const.py...
# from http://code.activestate.com/recipes/65207-constants-in-python
class _const:
    class ConstError(TypeError): pass  # Base exception class.
    class ConstCaseError(ConstError): pass

    def __setattr__(self, name, value):
        if name in self.__dict__:
            raise self.ConstError("Can't change const.%s" % name)
        if not name.isupper():
            raise self.ConstCaseError('const name %r is not all uppercase' % name)
        self.__dict__[name] = value

# Replace module entry in sys.modules[__name__] with instance of _const
# (and create additional reference to it to prevent its deletion -- see
#  https://stackoverflow.com/questions/5365562/why-is-the-value-of-name-changing-after-assignment-to-sys-modules-name)
import sys
_ref, sys.modules[__name__] = sys.modules[__name__], _const()

if __name__ == '__main__':
    import __main__  as const  # Test this module...

    try:
        const.Answer = 42  # Not OK to create mixed-case attribute name.
    except const.ConstCaseError as exc:
        print(exc)
    else:  # Test failed - no ConstCaseError exception generated.
        raise RuntimeError("Mixed-case const names should't be allowed!")

    try:
        const.ANSWER = 42  # Should be OK, all uppercase.
    except Exception as exc:
        raise RuntimeError("Defining a valid const attribute should be allowed!")
    else:  # Test succeeded - no exception generated.
        print('const.ANSWER set to %d raised no exception' % const.ANSWER)

    try:
        const.ANSWER = 17  # Not OK, attempt to change defined constant.
    except const.ConstError as exc:
        print(exc)
    else:  # Test failed - no ConstError exception generated.
        raise RuntimeError("Shouldn't be able to change const attribute!")

输出：

const name 'Answer' is not all uppercase
const.ANSWER set to 42 raised no exception
Can't change const.ANSWER