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...

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