[Tutor] Need help with the property function

[Dave Angel]

On 01/-10/-28163 02:59 PM, Jim Byrnes wrote:
> I'm trying to teach myself OOP in python (again). The following code
> from Dawson's book runs fine, unaltered [1].
>
> class Critter(object):
> """ A virtual pet """
> def __init__(self, name):
> print "A new critter is born"
> self.name = name
>
> def get_name(self):
> return self.__name
>
> def set_name(self, new_name):
> if new_name == "":
> print "A critters name cant be the empty string"
> else:
> self.__name = new_name
> print "Name change successful"
>
>
> name = property(get_name, set_name) #[1]
> # name = property(get_name) #[2]
> #different_name = property(get_name) #[3]
>
> def talk(self):
> print "Hi. I'm", self.name
>
> If I change [1] to [2] I get:
>
> Traceback (most recent call last):
> File "propertycritter.py", line 26, in <module>
> crit = Critter("Poochie")
> File "propertycritter.py", line 7, in __init__
> self.name = name
> AttributeError: can't set attribute
>
> If I change [1] to [3] the program runs with no errors.
>
> Could someone please explain why I am seeing these results.
>
> Thanks, Jim
>

In case#2 you're making name a read-only property.  So why on earth 
would you expect to be able to modify that property?

DaveA