On 2016-10-12 16:29, Travis Scrimshaw wrote:
>
>
> On Wednesday, October 12, 2016 at 9:01:51 AM UTC-5, Daniel Krenn wrote:
>
> On 2016-10-12 13:39, Jori Mäntysalo wrote:
> > More about this: In posets.py there is
> >
> > try:
> > elements = D.topological_sort()
> > except Exception:
> > raise ValueError("Hasse diagram contains cycles.")
> >
> > and that should be "except TypeError", as that is what
> > .topological_sort() raises from DiGraph that is not acyclic.
> >
> > But should a function without parameters like foo.bar() ever raise
> > TypeError? If we can run that, then the object foo is of the right
> type
> > and has bar()-function. Or where goes the limit between TypeError and
> > ValueError, i.e. what we mean by 'type' -- is DAG a "type" or just a
> > DiGraph with some special properties?
>
> There could be a ContainsCycleError which has RuntimeError as a base...
>
>
> IMO a ValueError is better than a TypeError because topological_sort
> (implicitly) takes the DiGraph as an input, and the input type is
> correct, just its value is wrong. Although this is more towards
> bikeshedding...
I agree that a ValueError is better than a TypeError. IMHO even better
is a (special) RuntimeError, as checking if it contains a cycle needs
(at least somehow) the sorting. Thus it happens when the algorithm has
already started. (bikeshedding... ;) )
Daniel
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