On Thu, 2007-03-15 at 00:09 +1100, Edward d'Auvergne wrote: > On 3/14/07, Chris MacRaild <[EMAIL PROTECTED]> wrote: > > On Tue, 2007-03-13 at 19:51 +1100, Edward d'Auvergne wrote: > > > Gary, > > > > > > I've written some unit tests which are located in the file > > > 'test_suite/unit_tests/data/__init__.py'. Would you know what > > > modifications I need to apply to make these tests run? These tests > > > are for the methods of the Data singleton class (the relax data > > > storage object) which is located in 'data/__init__.py'. I haven't > > > used the statement 'from x import Data' for this class so it is the > > > legal and ubiquitous usage of an __init__.py file. Would > > > 'unit_test_runner.py' handle this code? > > > > > > Thanks, > > > > > > Edward > > > > > > > > > P.S. These tests demonstrate the utility of subclassing the singleton > > > and is one reason I was arguing for the use of the class import rather > > > than reference import. > > > > > > > It is of course correct that the Singleton implimentation I proposed > > does not allow for subclassing. This however might well be seen as a > > design feature, given the well known conceptual problems with > > subclassing Singleton. Essentially, subclassing violates the Singleton > > Design Pattern: > > > > class Singleton: > > def __new__(self): > > ... > > > > class Sub(Singleton): pass > > > > >>> a = Singleton() > > >>> b = Sub() > > >>> isinstance(a,Singleton) > > True > > >>> isinstance(b,Singleton) > > True > > >>> a is b > > False > > >>> a == b > > False > > > > ie. we have 2 instances of Singleton that are not the same thing, and > > not even equal! If this is the behaviour you want, then you need > > something other than Singleton. On the other hand, if you really want > > Singleton, then you can't also hope for subclassability. > > Actually one is an instance of Singleton and the other is an instance > of Sub.
The definition of inheritance is that an instance of the subclass is also an instance of the parent class. ie. b is an instance of both Sub and Singleton. Inheritance from a Singleton class is therefore a logical contradiction. My vote is for B Chris _______________________________________________ relax (http://nmr-relax.com) This is the relax-devel mailing list [email protected] To unsubscribe from this list, get a password reminder, or change your subscription options, visit the list information page at https://mail.gna.org/listinfo/relax-devel
