[Python-ideas] Properties for classes possible?

[Erik Bray]

On Thu, Aug 20, 2015 at 11:57 AM, Sven R. Kunze <srkunze at mail.de> wrote:
> On 20.08.2015 17:31, Thomas Güttler wrote:
>>
>> The following solution provides an @classproperty:
>>  http://stackoverflow.com/a/5191224/633961
>>
>> I have not tried setting the value yet, but getting the
>> value works very fine.
>>
>> It would be great to have "@classproperty" even in Python2. Or at least
>> installable via pip.
>>
>> I am just a user in this case. I don't know about the best, cleanest, most
>> efficient
>> way to implement this.
>
>
> Reminds me of cached_property:
> https://pypi.python.org/pypi/cached-property/0.1.5
>
> I feel it could be useful to have a holistic solution (property + cached +
> instance,classes,modules) in the stdlib/Python somehow.

Having something like a cached-property (or the lazy=True option in my
classproperty implementation) is rather nice, but as Guido points out
it's out of scope for a general implementation of @classproperty (it's
also easy enough to implement memoization patterns outside the
stdlib).

However, for (settable) @classproperty to work seamlessly, without
having to involve custom metaclasses, would require a CPython
implementation and probably a PEP.  For in order for this to work it
would have to be special-cased, since assignments to a class attribute
don't normally go through <descriptor>.__set__.

Erik