Steven D'Aprano wrote:
> As I said, I haven't had a chance to try Peter's code, so it's possible
> that he's solved all these problems. I'm judging by previous
No, my simple code only "works" for read-only properties and only as long as
you don't overwrite the property by assigning to the attribute. To disallow
writing you can define a
def __set__(*args):
raise AttributeError
method, but that would only be invoked for instances of the class, not the
class itself. For the same reason the setter of a read/write class property
following that design would only be invoked in an instance, not in the
class.
The other simple solution, defining a normal property in the metaclass,
works for the class (as expected, remember that the class is an instance of
the metaclass), but is invisible to the instance:
>>> class T(type):
... @property
... def foo(self): return 42
...
>>> class Foo:
... __metaclass__ = T
...
>>> Foo.foo
42
>>> Foo.foo = "bar"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: can't set attribute
>>> Foo().foo
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'Foo' object has no attribute 'foo'
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