Cyclic class definations

[John Henry]

Thanks for the note, Nick.

I ended up with cycles as a historical reason.  Some code that were
written long time ago did not anticipate that part of it will get
sub-classed.

Thanks again.

Nick Vatamaniuc wrote:
> John,
> Cycles are tricky. Python is an interpreted dynamic language, whatever
> object you instantiate in your methods is a different thing than class
> hierarchy. Your class hierarchy is fine: ClassA->ClassASubclass->ClassC
> and it should work.  If it doesn't, create a quick mock example and
> post it along with the error.
>
> In general try to model your problem to avoid cycles if possible, I
> know sometimes they are un-avoidable, but more often then not, they
> are. Python might or might not allow cycles in certain situations
> (packages, imports, class hierarchy and during usage i.e. in your
> semantics) but regardless, if they make your code hard to understand so
> try to not introduce them if possible.
>
> Hope this helps,
> Nick V.
>
>
> John Henry wrote:
> > Hi list,
> >
> > I am trying to understand better Python packaging.  This might be a
> > messed up class hierachy but how would I break this cyclic relatioship?
> >
> > In file A:
> >
> > from B import B_Class
> >
> > Class_A_Main():
> >    def ....
> >    def SomeMethod(self):
> >       res=B_Class(self)
> >
> > Class_A_SubClass(Class_A_Main):
> >    def ...
> >
> >
> > In file B:
> >
> > Class B_Class():
> >    def __init__(self,parent):
> >       ...
> >    def SomeMethod(self):
> >       res=C_Class(self)
> >
> >
> > In file C:
> >
> > from file A import Class_A_SubClass
> >
> > Class C_Class(Class_A_SubClass):
> >    def __init__(self, parent):
> >       ...
> >
> >
> > As you can see, the cyclic relationship exists because C_Class is a
> > sub-class of SubClass which is in turn a sub-class of Class_A_Main and
> > in one of the methods of Class_A, it has a need to create a C_Class
> > object.
> >
> > I tried to merge the files A and C (by placing C_Class behind A_Class)
> > and have the method in A_Class create C_Class directly but that doesn't
> > work because Python says C_Class is not defined when it's processing
> > the A_Class method.   May be somebody can tell me how to "forward
> > declare" a class?
> > 
> > Regards,