determine_backend(value, dispatch_type, *, domain, only=True, coerce=False)

This is useful for functions that call multimethods without any dispatchable arguments. You can use determine_backend to ensure the same backend is used everywhere in a block of multimethod calls.

Notes

Support is determined by the __ua_convert__ protocol. Backends not supporting the type must return NotImplemented from their __ua_convert__ if they don't support input of that type.

Parameters

value :

The value being tested

dispatch_type :

The dispatch type associated with value , aka " marking <MarkingGlossary> ".

domain: string :

The domain to query for backends and set.

coerce: bool :

Whether or not to allow coercion to the backend's types. Implies only .

only: bool :

Whether or not this should be the last backend to try.

Set the backend to the first active backend that supports value

See Also

set_backend

For when you know which backend to set

Examples

Suppose we have two backends BackendA and BackendB each supporting different types, TypeA and TypeB . Neither supporting the other type:

This example is valid syntax, but raise an exception at execution

>>> with ua.set_backend(ex.BackendA):
...     ex.call_multimethod(ex.TypeB(), ex.TypeB())
Traceback (most recent call last):
    ...
uarray.BackendNotImplementedError: ...

Now consider a multimethod that creates a new object of TypeA , or TypeB depending on the active backend.

This example is valid syntax, but raise an exception at execution

>>> with ua.set_backend(ex.BackendA), ua.set_backend(ex.BackendB):
...         res = ex.creation_multimethod()
...         ex.call_multimethod(res, ex.TypeA())
Traceback (most recent call last):
    ...
uarray.BackendNotImplementedError: ...

res is an object of TypeB because BackendB is set in the innermost with statement. So, call_multimethod fails since the types don't match.

Instead, we need to first find a backend suitable for all of our objects.

This example is valid syntax, but raise an exception at execution

>>> with ua.set_backend(ex.BackendA), ua.set_backend(ex.BackendB):
...     x = ex.TypeA()
...     with ua.determine_backend(x, "mark", domain="ua_examples"):
...         res = ex.creation_multimethod()
...         ex.call_multimethod(res, x)
TypeA

See :

Back References

The following pages refer to to this document either explicitly or contain code examples using this.

scipy._lib._uarray._backend.determine_backend scipy._lib._uarray._backend.determine_backend_multi

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GitHub : /scipy/_lib/_uarray/_backend.py#543
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