On 6/1/21, Jon Ribbens via Python-list <python-list@python.org> wrote:
>
> I already answered that in the post you are responding to, but you
> snipped it: You can tell something's definitely not a data attribute
> if you have to put brackets after its name to call it as a method to
> invoke its function or retrieve the value it returns.
I prefer to use the generic term "computed attribute", which doesn't
interfere with the use of "data" in Python's concept of a data
descriptor and instance data. All descriptors are accessed without
calling them. Usually a non-data descriptor returns a bound callable
object, such as a method. But it can return anything. For example,
take the following P descriptor type:
class P:
def __get__(self, obj, cls):
if obj is not None:
return 42
return self
class C:
p = P()
obj = C()
>>> obj.p
42
The P type doesn't implement __set__ or __delete__, so it's not a data
descriptor. This means we can set instance data `p` that overrides the
computed attribute. For example:
>>> obj.p = 21
>>> vars(obj)
{'p': 21}
>>> obj.p
21
>>> del obj.p
>>> obj.p
42
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