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Update type casting section for interaction with Python scalars #74

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Nov 10, 2020
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Update type casting section for interaction with Python scalars #74

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2 changes: 2 additions & 0 deletions spec/API_specification/array_object.md
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Expand Up @@ -15,6 +15,8 @@ A conforming implementation of the array API standard must provide and support a

* * *

(operators)=

## Operators

A conforming implementation of the array API standard must provide and support an array object supporting the following Python operators:
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29 changes: 29 additions & 0 deletions spec/API_specification/type_promotion.md
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Expand Up @@ -18,6 +18,11 @@ In code, use the data type objects specified in {ref}`data-types` (e.g., `int16`

<!-- Note: please keep table columns aligned -->

The following type promotion tables specify the casting behaviour for
operations involving two arrays. In situations where more than two arrays
participate, the table can be used repeatedy on pairs of input arrays (the
result does not depend on the order in which the arrays are given).

### Signed integer type promotion table

| | i1 | i2 | i4 | i8 |
Expand Down Expand Up @@ -82,3 +87,27 @@ where
Mixed integer and floating-point type promotion rules are not specified
because behavior varies between implementations.
```

### Mixing arrays with Python scalars

Using Python scalars (i.e. instances of `bool`, `int`, `float`) together with arrays must be supported for:

- `array <op> scalar`,
- `scalar <op> array`,

where `<op>` is a built-in operator (see {ref}`operators` for operators
supported by the array object), and `scalar` is of the same kind as the array
dtype (e.g. a `float` scalar if the array's dtype is `float32` or `float64`).
The expected behaviour is then equivalent to:

1. Convert the scalar to a 0-D array with the same dtype as that of the array
used in the expression.
2. Execute the operation for `array <op> 0-D array` (or `0-D array <op>
array` if `scalar` was the left-hand argument).

```{note}

Note again that mixed integer and floating-point behaviour is not specified.
Mixing an integer array with a Python float may give `float32`, `float64`,
or raise an exception - behaviour of implementations will differ.
```