.. automodule:: uarray .. rubric:: Functions .. autosummary:: :toctree: all_of_type create_multimethod generate_multimethod mark_as set_backend set_global_backend register_backend clear_backends skip_backend wrap_single_convertor .. rubric:: Classes .. autosummary:: :toctree: Dispatchable .. rubric:: Exceptions .. autosummary:: :toctree: BackendNotImplementedError
The following section discusses the design philosophies of :obj:`uarray`, and the reasoning behind some of these philosophies.
:obj:`uarray` (and its sister modules :obj:`unumpy` and others to come) were designed from the ground-up to be modular. This is part of why :obj:`uarray` itself holds the core backend and dispatch machinery, and :obj:`unumpy` holds the actual multimethods. Also, :obj:`unumpy` can be developed completely separately to :obj:`uarray`, although the ideal place to have it would be NumPy itself.
However, the benefit to having it separate is that it could span multiple NumPy versions, even before NEP-18 (or even NEP-13) was available. Another benefit is that it can have a faster release cycle to help it achieve this.
Code wishing to use the backend machinery for NumPy (as an example) will
use the statement
import unumpy as np instead of the usual
import numpy as np. This is deliberate: it makes dispatching opt-in
instead of being forced to use it, and the overhead associated with it.
However, a package is free to define its main methods as the dispatchable
versions, thereby allowing dispatch on the default implementation.
Extensibility and Choice
If some effort is put into the dispatch machinery, it's possible to dispatch over arbitrary objects --- including arrays, dtypes, and so on. A method defines the type of each dispatchable argument, and backends are only passed types they know how to dispatch over, when deciding whether or not to use that backend. For example, if a backend doesn't know how to dispatch over dtypes, it won't be asked to decide based on that front.
Methods can have a default implementation in terms of other methods, but they're still overridable.
This means that only one framework is needed to, for example, dispatch
ufunc s, arrays, dtypes and all other primitive objects in NumPy,
while keeping the core :obj:`uarray` code independent of NumPy and even
Backends can span modules, so SciPy could jump in and define its own methods on NumPy objects and make them overridable within the NumPy backend.
The users of :obj:`unumpy` or :obj:`uarray` can choose which backend they want to prefer with a simple context manager. They also have the ability to force a backend, and to skip a backend. This is useful for array-like objects that provide other array-like objects by composing them. For example, Dask could perform all its blockwise function calls with the following psuedocode (obviously, this is simplified):
in_arrays = extract_inner_arrays(input_arrays) out_arrays =  for input_arrays_single in in_arrays: args, kwargs = blockwise_function.replace_args_kwargs( args, kwargs, input_arrays_single) with ua.skip_backend(DaskBackend): out_arrays_single = blockwise_function(*args, **kwargs) out_arrays.append(out_arrays_single) return combine_arrays(out_arrays)
A user would simply do the following:
with ua.use_backend(DaskBackend): # Write all your code here # It will prefer the Dask backend
There is no default backend, to :obj:`unumpy`, NumPy is just another backend. One can register backends, which will all be tried in indeterminate order when no backend is selected.
Addressing past flaws
The progress on NumPy's side for defining an override mechanism has been slow, with
NEP-13 being first introduced in 2013, and with the wealth of dispatchable objects
(including arrays, ufuns and dtypes), and with the advent of libraries like Dask,
CuPy, Xarray, PyData/Sparse and XND, it has become clear that the need for alternative
array-like implementations is growing. There are even other libraries like PyTorch, and
TensorFlow that'd be possible to express in NumPy API-like terms. Another example
includes the Keras API, for which an overridable
ukeras could be created, similar
:obj:`uarray` is intended to have fast development to fill the need posed by these communities, while keeping itself as general as possible, and quickly reach maturity, after which backwards compatibility will be guaranteed.
Performance considerations will come only after such a state has been reached.