Steven Bethard <steven.bethard <at> gmail.com> writes: > > David S. wrote: > > I am looking for a way to implement the same simple validation on many > > instance attributes and I thought descriptors > > (http://users.rcn.com/python/download/Descriptor.htm) looked like the > > right tool. > > > Looks like you're trying to reinvent the property descriptor. Try using > the builtin property instead: > > py> def getchar(self): > ... if not hasattr(self, '_char'): > ... self._char = None > ... return self._char > ... > py> def setchar(self, value): > ... if not len(value) == 1: > ... raise ValueError > ... self._char = value > ... > py> singlechar = property(getchar, setchar) > py> class Flags(object): > ... a = singlechar > ... b = singlechar > ... > py> f = Flags() > py> f.a = "a" > py> f.b = "bb" > Traceback (most recent call last): > File "<interactive input>", line 1, in ? > File "<interactive input>", line 3, in setchar > ValueError > This still fails to work for instances variables of the class. That is if I use your property in the following: py> ...class Flags(object): ... def __init__(self): ... a = singlechar ... py> f = Flags() py> f.a = "a"
Now f.a.__class__.__name__ returns 'str'. So the property was not used at all. Also, it seems that using a property, I can not do the other useful things I can do with a proper class, like provide an __init__, __str__, or __repr__. Again, thanks, David S. -- http://mail.python.org/mailman/listinfo/python-list
