[Python-Dev] properties and block statement

Wed Oct 19 09:01:21 CEST 2005

on 18.10.2005 19:17 Antoine Pitrou said the following:
>> What would this mythical block statement look like that would make
>>properties easier to write than the above late-binding or the subclass
>>Property recipe?
>> I suppose something like:
>> class C(object):
> x = prop:
> """ Yay for property x! """
> def __get__(self):
> return self._x
> def __set__(self, value):
> self._x = x
>> and then:
>> def prop(@block):
> return property(
> fget=block.get("__get__"),
> fset=block.get("__set__"),
> fdel=block.get("__delete__"),
> doc=block.get("__doc__", ""),
> )
>> (where "@bargs" would be the syntax to refer to block args as a dict,
> the same way "**kargs" already exist)
>
I think there is no need for a special @syntax for this to work.
I suppose it would be possible to allow a trailing block after any 
function invocation, with the effect of creating a new namespace that 
gets treated as containing keyword arguments.
No additional function needed for the property example::
 class C(object):
 x = property():
 doc = """ Yay for property x! """
 def fget(self):
 return self._x
 def fset(self, value):
 self._x = x
(This does not help with the problem of overridability though...)
A drawback is that such a "keyword block" would only be possible for the 
last function invocation of a statement.
Although the block could also be inside the method invocation 
parentheses? I do not think that this is a pretty sight but I'll spell 
it out anyways ;-) ::
 class C(object):
 x = property(:
 doc = """ Yay for property x! """
 def fget(self):
 return self._x
 def fset(self, value):
 self._x = x
 )
--stefan