Use __slots__ they will simply give you an error. But at the same time I don't think they are inheritable and in general you should only use slots for performance reasons (even then test before using).
Or you could also simulate a __slots__ mechanism the way you are doing i.e. checking the attributes yourself. But I would suggest though that you create a test case (unittest) and run testing _separately_ from your code. Your code should do only what it does, too many "if i messed: up warn me" or "need to make sure I don't have extra attributes" checks would make the code itself incomprehnsible over time as half of it would end up being just checks for exceptional situations. So spend 5 minutes to look up http://pyunit.sourceforge.net/ and then in the long run your effort to implement testing will be rewarded. Nick V. Matthew Wilson wrote: > I sometimes inadvertently create a new attribute on an object rather > update a value bound to an existing attribute. For example: > > In [5]: class some_class(object): > ...: def __init__(self, a=None): > ...: self.a = a > ...: > > In [6]: c = some_class(a=1) > > In [7]: c.a > Out[7]: 1 > > In [8]: c.A = 2 > > I meant to update c.a but I created a new c.A. I make this mistake > probably hourly. > > I suspect adding attributes at run time can be a beautiful thing, but in > this particular instance, I'm only using this feature to hurt myself. > > I wrote a simple class that will warn me when I make this mistake in the > future: > > import warnings > > class C(object): > > warn_on_new_attributes = True > > standard_attributes = [] > > def __setattr__(self, name, value): > > if self.warn_on_new_attributes \ > and name is not 'warn_on_new_attributes' \ > and name not in self.standard_attributes: > > warnings.warn("%s has no standard attribute %s." > % (self.__class__.__name__, name)) > > > self.__dict__[name] = value > > > class C1(C): > > standard_attributes = ['a1', 'a2'] > > > class C2(C): > > warn_on_new_attributes = False > > # Do some simple testing. > c11 = C1() > c11.a1 = 1 > c11.a2 = 2 > c11.a3 = 3 > c11.a4 = 4 > > # Disable warnings for this instance. > c12 = C1() > c12.warn_on_new_attributes = False > c12.a1 = 1 > c12.a2 = 2 > c12.a3 = 3 > c12.a4 = 4 > > c11.a5 = 5 > > # Use an object that has warnings disabled by default. > c2 = C2() > c2.a1 = 1 > c2.a2 = 2 > c2.a3 = 3 > c2.a4 = 4 > > # enable warnings for this object. > c2.warn_on_new_attributes = True > c2.a1 = 1 > c2.a5 = 5 > > > All comments are welcome. Is there a better way of implementing the > above class, OR, is this approach generally wrong-headed? Am I the only > one that makes this mistake? > > TIA > > -- > A better way of running series of SAS programs: > http://overlook.homelinux.net/wilsonwiki/SasAndMakefiles -- http://mail.python.org/mailman/listinfo/python-list
