On Wed, Dec 2, 2020 at 3:39 PM Sebastian Berg <sebast...@sipsolutions.net> wrote:
> 1. If an argument is invalid in NumPy it is considered and error. > For example: > > np.log(arr, my_weird_argument=True) > > is always an error even if the `__array_function__` implementation > of `arr` would support it. > NEP 18 explicitly says that allowing forwarding could be done, but > will not be done at this time. > >From my perspective, this is a good thing: it ensures that NumPy's API is only used for features that exist in NumPy. Otherwise I can imagine causing considerable confusion. If you want to use my_weird_argument, you can call my_weird_library.log() instead. > 2. Arguments must only be forwarded if they are passed in: > > np.mean(cupy_array) > > ends up as `cupy.mean(cupy_array)` and not: > > cupy.mean(cupy_array, axis=None, dtype=None, out=None, > keepdims=False, where=True) > > meaning that CuPy does not need to implement all of those kwargs and > NumPy can add new ones without breaking anyones code. > My reasoning here was two-fold: 1. To avoid the unfortunate situation for functions like np.mean(), where NumPy jumps through considerable hoops to avoid passing extra arguments in an ad-hoc way to preserve backwards compatibility 2. To make it easy for a library to implement "incomplete" versions of NumPy's API, by simply omitting arguments. The idea was that NumPy's API is open to partial implementations, but not extension. > 3. NumPy should not check the *validity* of the arguments. For example: > `np.add.reduce(xarray, axis="long")` should probably work in xarray. > (`xarray.DataArray` does not actually implement the above.) > But a string cannot be used as an axis in NumPy. > I don't think libraries should be encouraged to abuse NumPy's API to mean something else. Certainly I would not use this in xarray :). If we could check the validity of arguments cheaply, that would be fine by me. But I didn't think it was worth adding overhead to every function call. Perhaps type annotations could be relied on for these sorts of checks? I am pretty happy considering not checking the validity of arguments to be an implementation detail for now.
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