Class RingChangeScreen

BaseScreen.BaseScreen --+
                        |
                       RingChangeScreen

>>> screen = RingChangeScreen([5,6],True)
>>> screen.screenSmiles("C=CC=C.C=C>>C1CC=CCC1");
True
>>> screen.screenSmiles("N=[N+]=[N-].C#C>>c1cnn[nH]1");
True
>>> screen.screenSmiles("C.C=C>>C1CC1");
False
>>> screen.screenSmiles("CC.C=C>>C1CCC1");
False
>>> screen.screenSmiles("C1CC=CCC1>>C=CC=C.C=C");
False
>>> screen.screenSmiles("c1cnn[nH]1>>N=[N+]=[N-].C#C");
False

>>> screen = RingChangeScreen([6, 5],False)
>>> screen.screenSmiles("C=CC=C.C=C>>C1CC=CCC1");
False
>>> screen.screenSmiles("N=[N+]=[N-].C#C>>c1cnn[nH]1");
False
>>> screen.screenSmiles("C.C=C>>C1CC1");
False
>>> screen.screenSmiles("CC.C=C>>C1CCC1");
False
>>> screen.screenSmiles("C1CC=CCC1>>C=CC=C.C=C");
True
>>> screen.screenSmiles("c1cnn[nH]1>>N=[N+]=[N-].C#C");
True

Constructor.  
ringSizes 
    is a list specifying the 
    ring sizes to be considered.  For example, [5,6] for
    5 and 6 membered rings.
formation
    Indicates if the screen is to allow reactions where
    there is "formation" of the indicated ring size.
    That is, where there are more such rings in the products
    than reactants.  If false, will instead look for
    "destruction" where there are fewer such rings in the
    products than reactants.