Bryan schrieb:
On Nov 13, 9:34 am, "Diez B. Roggisch" <de...@nospam.web.de> wrote:
Bryan schrieb:
I have several properties on a class that have very similar behavior.
If one of the properties is set, all the other properties need to be
set to None. So I wanted to create these properties in a loop like:
class Test(object):
for prop in ['foo', 'bar', 'spam']:
# Attribute that data is actually stored in
field = '_' + prop
# Create getter/setter
def _get(self):
return getattr(self, field)
def _set(self, val):
setattr(self, field, val)
for otherProp in prop:
if otherProp != prop: setattr(self, '_' + otherProp,
None)
# Assign property to class
setattr(Test, prop, property(_get, _set))
t = Test()
t.foo = 1
assert t.bar == t.spam == None
But the class Test is not defined yet, so I can't set a property on
it. How can I do this?
With a metaclass, or a post-class-creation function. Which is a
metaclass without being fancy.
Just put your above code into a function with the class in question as
argument, and invoke it after Test is defined.
Diez
I think there are some closure issues with this as I am getting very
strange results. I think all properties have the getter/setters of
whatever the last item in the list was.
t.foo = 'settingFoo' actually sets t.spam, as 'spam' was the last
property generated.
That's a FAQ. Closures capture the *names*, not the values. There are
various options to remedy this, e.g. by something like this:
def gen_property(prop):
def _get(...) # your code
return property(_get, _set)
setattr(Test, prop, gen_property(prop))
Diez
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