Knacktus wrote:
Hi guys,
I've got the following (not working) code:
[...]
The problem is that the descriptors are created when the module is
evaluated. But at this time the class BaseItem is not known yet. Any ideas?
Yes -- don't do that.
What are you actually trying to accomplish? Embedding an instance of the
class in the class is a means to an end, not the end itself. What
problem are you trying to solve? There may be a better way.
My *guess* is that you're trying to create properties that automatically
check their type. As much as I think that's probably a bad idea, this is
how I would solve that:
import functools
class CheckedProperty(property):
def __init__(self, type, fget=None, fset=None, fdel=None, doc=None):
if fset is not None:
fset = self.checked(type, fset)
super().__init__(fget, fset, fdel, doc)
def checked(self, type, func):
@functools.wraps(func)
def inner(self, value):
if not isinstance(value, type):
raise TypeError('invalid type')
return func(self, value)
return inner
class Test(object):
def _getx(self):
return self.__x
def _setx(self, value):
self.__x = value
x = CheckedProperty(str, _getx, _setx)
But please don't over-use isinstance checks. They're a bad idea.
--
Steven
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