Python：如何克服使用特殊方法的损坏变量的锁？

Question

In python, one is able to use special methods to achieve something similar to operator overloading in C++ by defining a special method for __setattr__. I have seen some coders use this to create a read-only lock using a mangled variable name. That's pretty clever until I need to an element to an array of the locked class. For example, FreeIPA implements this . This would be fairly straightforward to defeat by simply setting exampleArray._ReadOnly__locked = False, except this is ALSO caught by the __setattr__ special method and results in the error

"ipa: ERROR: AttributeError: locked: cannot set NameSpace._ReadOnly__locked to False"

Is there a simple and clever way to set this back to read-write mode so that I can insert my value into the array?

Answer 1

As noted in the docstring, you can use the default implementation of __setattr__ from object .

class ReadOnly(object):
    def __setattr__(self, name, value):
        raise AttributeError("This instance is read only.")

r = ReadOnly()
object.__setattr__(r, 'name', 'value')
print r.name # 'value'

The potential issue here is when your parent class does something special when setting objects. In this case, your resulting instance may be inconsistent.