[Python-ideas] Re: Add a decorators called @staticproperty

18 Dec 2021

      I'm confused about what a staticproperty would even be.

Usually, properties are a way to provide an  interface that "looks like" a
simple attribute, but does some computation under the hood. But that
computation usually requires instance data to do its thing -- so a static
one wouldn't be useful.

In fact, in Python, a staticmethod is not very useful at all anyway, all it
is is a function that lives in the class namespace. Making it a property
would make it look like a class attribute.

Hmm, I guess one use case would be to make a read only class attribute.

Anyway, the thing is that both staticmethod and property are implimented
using descriptors, which I think can only be invoked by instance attribute
lookup. That is, the class attribute IS a descriptor instance.

And Chris A says -- there may be a way to get a similar effect with
Metaclasses, but we'd have to know what your goal is to advise on how to do
that.

Note: you can put a descriptor on class, and the __get__ will be called, to
get part of what I think you want:

In [52]: class Ten:
    ...:     def __get__(self, obj, objtype=None):
    ...:         return 10
    ...:     def __set__(self, obj, value):
    ...:         raise AttributeError("attribute can not be set")
    ...:

In [53]: class A:
    ...:     y = Ten()
    ...:

# attribute access does call the descriptor's __get__:

In [54]: A.y
Out[54]: 10

But setting the attribute replaces the descriptor, rather than raising an
exception:

In [55]: A.y = 12

In [56]: A.y
Out[56]: 12

Honestly, I don't quite "get" how all this works, but the usual thing is
for Descriptors to be invoked on instance attribute access.

-CHB

On Sat, Dec 18, 2021 at 8:30 AM <me@chenjt.com> wrote:
...
In the following situations:
class Data(object):
    @staticmethod
    @property
    def imagesTotal():
        return 10
print(Data.imagesTotal)
The "print(Data.imagesTotal)" can't print "10", it print "<property object
at 0x...>".
It might be a good idea to use "@staticproperty" to solve this problem.
"@staticproperty" is a decorators, it mix the @staticmethod and @property.
Then the static property has getter and setter.
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