Question

In Python, I want to make selected instance attributes of a class be readonly to code outside of the class. I want there to be no way outside code can alter the attribute, except indirectly by invoking methods on the instance. I want the syntax to be concise. What is the best way? (I give my current best answer below…)

Answer 1

You should use the @property decorator.

>>> class a(object): ...     def __init__(self, x): ...             self.x = x ...     @property ...     def xval(self): ...             return self.x ...  >>> b = a(5) >>> b.xval 5 >>> b.xval = 6 Traceback (most recent call last):   File '<stdin>', line 1, in <module> AttributeError: can't set attribute