[Python] Python descriptors on Readonly attributes

I want to refactor a big part of my code into a generic descriptor for read only attribute access. The following is an example of property based implementation

class A:
def __init__(self, n):
self._n = n
self._top = -1

@property
def n(self):
return self._n

@property
def top(self):
return self._top

def increase(self):
self._top += 1


you see I can initialize my A class and increase self._top but not to let user set a.top by omitting property setter method

a = A(7)
a.top
Out[25]: -1
a.increase()
a.top
Out[27]: 0


if I do a.top = 4, it will give me an error

AttributeError: property 'top' of 'A' object has no setter


which is expected. Now, I want to refactor this logic into a descriptor

class ReadOnly:

def __init__(self):
self._name = None

def __set_name__(self, owner, name):
self._name = name

def __get__(self, instance, owner):
if instance is None:
return self
return instance.__dict__[self._name]

def __set__(self, instance, value):
raise AttributeError("Can't set attribute")

def __delete__(self, instance):
raise AttributeError("Can't delete attribute")

class A:
n = ReadOnly()
top = ReadOnly()

def __init__(self, n):
self.n = n
self.top = -1

def increase(self):
self.top += 1


Well, this doesn't work. I can't even initialize the class A anymore, cause in __init__ it will set n and top immediately and prevent my from initialize.

How to write this logic from property into descriptor?

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