bruno.42.desthuilliers at websiteburo
Jul 10, 2009, 3:38 AM
Post #8 of 8
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Bruno Desthuilliers a écrit :
(snip)
> You could write your own custom descriptor. Or just use an additional
> level of indirection, ie:
>
> myProperty = property(lambda self: self.myClassMethod())
>
Sorry, looks like I didn't read carefully enough. The above code won't
work if you intend to lookup the property directly on the class object,
ie "MyClass.myProperty". If that was your intention, you'll need a
custom descriptor. The following code should do the job, or at least get
you started:
# python 2.5.x
# the custom (non binding) descriptor
class ClsProperty(object):
def __init__(self, fget):
if not isinstance(fget, (classmethod, staticmethod)):
# XXX better error message
raise ValueError(
"fget must be a classmethod or staticmethod"
)
self.fget = fget
def __get__(self, obj, cls=None):
if cls is None:
assert obj is not None
cls = type(obj)
return self.fget.__get__(obj, cls)()
# helper -> a simple decorator
def classproperty(func):
if not isinstance(func, (classmethod, staticmethod)):
func = classmethod(func)
return ClsProperty(func)
# example use
class Foo(object):
# the hard way
@classmethod
def bar(cls):
return "%s.bar" % cls.__name__
quux = ClsProperty(bar)
# the simple way
@classproperty
def baaz(cls):
return "%s.baaz" % cls
Given your example, this should be enough. If you need a binding
descriptor (one with a setter), you'll have to implement the __set__
method (and possibly __del__). Google for "python descriptor" to find
more doc about the descriptor protocol.
HTH
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