On 24 August 2017 at 10:28, Thomas Kluyver <tho...@kluyver.me.uk> wrote:
> On Thu, Aug 24, 2017, at 02:21 PM, xoviat wrote: > > I mean is this golang or Python? In Python, you raise notimplementederror. > > > But there's a NotImplemented singleton in Python as well. The argument for > using a return value is that the hook code has to deliberately return that, > whereas a NotImplementedError could bubble up from some internal call, in > which case it should really be registered as an error. > This! And a backend that wanted a bubbled up NotImplementedError (or some other exception) to mean it actually doesn't support an operation, can catch the error and return. The ideal Pythonic way would be to raise a specific exception (something like PEP517UnsupportedOperation), but since it's not a builtin we would be left with the problem of defining it somewhere, which would become a dependency of all backends, and no, we don't want that. All this has been hashed and rehashed before. I think we can move on from this argument and define `return NotImplemented` as the way to define a backend operation as unsupported.
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