On Thu, Jul 2, 2020 at 8:38 PM Greg Ewing <[email protected]> wrote:
>
> On 2/07/20 9:45 pm, Chris Angelico wrote:
> > On Thu, Jul 2, 2020 at 7:41 PM Alex Hall <[email protected]> wrote:
> >>
> >> On Thu, Jul 2, 2020 at 11:33 AM Chris Angelico <[email protected]> wrote:
> >>>
> >>> What's the idea being discussed? AIUI there's no need or request to
> >>> change the language/stdlib, but maybe I'm misreading.
> >>
> >> Ah, now I understand. I did automatically assume that Greg was proposing
> >> adding this to the stdlib or something, but maybe I only assumed that
> >> because it was in the list.
> >
> > Could be that I'm the one misunderstanding here, but only Greg can
> > answer that question :)
>
> I was thinking something like it might become a candidate for stdlib
> inclusion, if it wasn't universally hated for abusing the class
> statement.
>
Let's get concrete then. Suppose that the property constructor
recognized a special one-argument form: if it has an fget attribute,
it fetches its details from the fget, fset, fdel, and __doc__
attributes of that object. That way, it can be used in three ways: a
standard constructor that does all the work with up to four arguments,
the decorator form (which is the same as the one-arg form initially,
but then you can use its setter decorator), and the class form.
class Test:
x = property(lambda self: 42, lambda self, val: print("Setting to", val))
@property
def y(self): return 42
@y.setter
def y(self, val): print("Setting to", val)
# the theoretical one
@property
class z:
def fget(self): return 42
def fset(self, val): print("Setting to", val)
Since functions won't normally have fset attributes, this should be
fairly safe - technically it'd be backward incompatible, but it's
highly unlikely to break any real-world code.
I don't write a lot of properties with setters, so I can't speak to
the value of this, but it is at least plausible.
(If you'd prefer to use "get" or "getter" or something in place of
"fget", that would work fine. I used the same name as the keyword arg
to property itself, but it can be anything.)
ChrisA
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