(l-onnx-doc-Optional)=

# Optional


(l-onnx-op-optional-15)=

## Optional - 15

### Version

- **name**: [Optional (GitHub)](https://github.com/onnx/onnx/blob/main/docs/Operators.md#Optional)
- **domain**: `main`
- **since_version**: `15`
- **function**: `False`
- **support_level**: `SupportType.COMMON`
- **shape inference**: `True`

This version of the operator has been available
**since version 15**.

### Summary

Constructs an optional-type value containing either an empty optional of a certain type specified by the attribute,
or a non-empty value containing the input element.

### Attributes

* **type - TYPE_PROTO** :

  Type of the element in the optional output

### Inputs

Between 0 and 1 inputs.

- **input** (optional, heterogeneous) - **V**:

  The input element.

### Outputs

- **output** (heterogeneous) - **O**:

  The optional output enclosing the input element.

### Type Constraints

* **V** in ( `seq(tensor(bool))`, `seq(tensor(complex128))`, `seq(tensor(complex64))`, `seq(tensor(double))`, `seq(tensor(float))`, `seq(tensor(float16))`, `seq(tensor(int16))`, `seq(tensor(int32))`, `seq(tensor(int64))`, `seq(tensor(int8))`, `seq(tensor(string))`, `seq(tensor(uint16))`, `seq(tensor(uint32))`, `seq(tensor(uint64))`, `seq(tensor(uint8))`, `tensor(bool)`, `tensor(complex128)`, `tensor(complex64)`, `tensor(double)`, `tensor(float)`, `tensor(float16)`, `tensor(int16)`, `tensor(int32)`, `tensor(int64)`, `tensor(int8)`, `tensor(string)`, `tensor(uint16)`, `tensor(uint32)`, `tensor(uint64)`, `tensor(uint8)` ):

  Constrain input type to all tensor and sequence types.
* **O** in ( `optional(seq(tensor(bool)))`, `optional(seq(tensor(complex128)))`, `optional(seq(tensor(complex64)))`, `optional(seq(tensor(double)))`, `optional(seq(tensor(float)))`, `optional(seq(tensor(float16)))`, `optional(seq(tensor(int16)))`, `optional(seq(tensor(int32)))`, `optional(seq(tensor(int64)))`, `optional(seq(tensor(int8)))`, `optional(seq(tensor(string)))`, `optional(seq(tensor(uint16)))`, `optional(seq(tensor(uint32)))`, `optional(seq(tensor(uint64)))`, `optional(seq(tensor(uint8)))`, `optional(tensor(bool))`, `optional(tensor(complex128))`, `optional(tensor(complex64))`, `optional(tensor(double))`, `optional(tensor(float))`, `optional(tensor(float16))`, `optional(tensor(int16))`, `optional(tensor(int32))`, `optional(tensor(int64))`, `optional(tensor(int8))`, `optional(tensor(string))`, `optional(tensor(uint16))`, `optional(tensor(uint32))`, `optional(tensor(uint64))`, `optional(tensor(uint8))` ):

  Constrain output type to all optional tensor or optional sequence types.