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https://github.com/waikato-datamining/fast-opex

Simpler and faster implementation of the OPEX JSON file format for object detection predictions.
https://github.com/waikato-datamining/fast-opex

exchange-format json object-detection

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Simpler and faster implementation of the OPEX JSON file format for object detection predictions.

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# fast-opex
Simpler and faster implementation of the OPEX JSON file format for object detection predictions.

Uses [orjson](https://github.com/ijl/orjson) if present (no pretty-printing available) for further speed-ups,
otherwise the standard json library.

This library is written in Python. For a Java port, please see
[opex4j](https://github.com/waikato-datamining/opex4j).

## Installation

You can install the library via `pip` (or `pip3`):

```commandline
pip install fast-opex
```

## JSON

```json
{
"timestamp": "%Y%m%d_%H%M%S.%f",
"id": "str",
"objects": [
{
"score": 1.0,
"label": "person",
"bbox": {
"top": 100,
"left": 100,
"bottom": 150,
"right": 120
},
"polygon": {
"points": [
[100, 100],
[150, 100],
[150, 120],
[100, 120]
]
}
},
{
"score": 0.95,
"label": "house",
"bbox": {
"top": 100,
"left": 100,
"bottom": 200,
"right": 200
},
"polygon": {
"points": [
[100, 100],
[200, 100],
[200, 200],
[100, 200]
]
},
"meta": {
"price": "500k"
}
}
],
"meta": {
"key1": "value1",
"key2": "value2"
}
}
```

**Notes:**

The following keys are optional:

* timestamp
* meta
* score

## Reading/Writing

To read a prediction:

```python
from opex import ObjectPredictions

# From a string
predictions = ObjectPredictions.from_json_string("{...}")

# From a named file
predictions = ObjectPredictions.load_json_from_file("predictions.json")

# From an open stream
with open("predictions.json", "r") as stream:
predictions = ObjectPredictions.read_json_from_stream(stream)
```

To write a prediction:

```python
from opex import ObjectPredictions

predictions: ObjectPredictions = ...

# Serialise the object to a JSON-formatted string
print(predictions.to_json_string())
print(predictions.to_json_string(indent=2))

# Write the object to a file
predictions.save_json_to_file("predictions.json", indent=2)

# Write to an open stream
with open("predictions.json", "w") as stream:
predictions.write_json_to_stream(stream, indent=2)
```