>>> class I(int):
...     @property
...     def a(self): pass
...     @property
...     def b(self): pass
...     @b.setter
...     def b(self, value): pass
...     @property
...     def c(self): pass
...     @c.deleter
...     def c(self): pass
... 
>>> obj = I()
>>> del obj.numerator
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: attribute 'numerator' of 'int' objects is not writable
>>> del obj.to_bytes
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: to_bytes
>>> del obj.from_bytes
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: from_bytes
>>> del obj.a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't delete attribute
>>> del obj.b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't delete attribute
>>> del obj.y
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: y
>>> obj.numerator = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: attribute 'numerator' of 'int' objects is not writable
>>> obj.a = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute
>>> obj.c = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute
>>> 
>>> obj = 1
>>> del obj.numerator
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: attribute 'numerator' of 'int' objects is not writable
>>> del obj.to_bytes
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object attribute 'to_bytes' is read-only
>>> del obj.from_bytes
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object attribute 'from_bytes' is read-only
>>> del obj.y
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'y'
>>> obj.numerator = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: attribute 'numerator' of 'int' objects is not writable
>>> obj.to_bytes = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object attribute 'to_bytes' is read-only
>>> obj.from_bytes = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object attribute 'from_bytes' is read-only
>>> obj.y = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'y'

Different error messages are used in errors when try to modify non-existing or read-only attribute. This depends on the existing __dict__ and the way how the attribute is resolved.

* just the attribute name
* "'%.50s' object has no attribute '%U'"
* "'%.50s' object attribute '%U' is read-only"
* "attribute '%V' of '%.100s' objects is not writable"

I think it would be nice to unify error messages and make them more specific.

> I think it would be nice to unify error messages and make them more specific.

How can they can be more specific when they are unified?

Not all error messages contain an attribute name, an object type name and a reason.