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# Ballista Python Bindings (PyBallista)

This is a Python library that binds to [Apache Arrow](https://arrow.apache.org/) distributed query
engine [Ballista](https://github.com/apache/arrow-ballista).

## Status

### What works?

- Start Ballista schedulers and executors from Python
- Execute distributed SQL queries (with DataFusion backend)
- Use DataFrame API to read files and execute distributed queries (with DataFusion backend)
- Support for CSV, Parquet, and Avro formats

### What does not work?

- Python UDFs
- JSON

## Roadmap

- Support reading JSON
- Support distributed Python UDFs and UDAFs
- Support distributed query execution against Python DataFrame libraries such as Polars, Pandas, and cuDF, that are
  already supported by DataFusion's Python bindings (this will require new features in Ballista)

## Examples

- [Query a Parquet file using SQL](./examples/sql-parquet.py)
- [Query a Parquet file using DataFrame API](./examples/dataframe-parquet.py)
- [Start a scheduler from within a Python process](./examples/run-scheduler.py)
- [Start an executor from within a Python process](./examples/run-executor.py)

## How to install (from pip)

```bash
pip install ballista
# or
python -m pip install ballista
```

## How to develop

This assumes that you have rust and cargo installed. We use the workflow recommended by [pyo3](https://github.com/PyO3/pyo3) and [maturin](https://github.com/PyO3/maturin).

Bootstrap:

```bash
# fetch this repo
git clone git@github.com:apache/arrow-ballista-python.git
# change to python directory
cd arrow-ballista-python
# prepare development environment (used to build wheel / install in development)
python3 -m venv venv
# activate the venv
source venv/bin/activate
# update pip itself if necessary
python -m pip install -U pip
# if python -V gives python 3.7
python -m pip install -r requirements-37.txt
# if python -V gives python 3.8/3.9/3.10
python -m pip install -r requirements-310.txt
```

Whenever rust code changes (your changes or via `git pull`):

```bash
# make sure you activate the venv using "source venv/bin/activate" first
maturin develop
python -m pytest
```

## How to update dependencies

To change test dependencies, change the `requirements.in` and run

```bash
# install pip-tools (this can be done only once), also consider running in venv
python -m pip install pip-tools

# change requirements.in and then run
python -m piptools compile --generate-hashes -o requirements-37.txt
# or run this is you are on python 3.8/3.9/3.10
python -m piptools compile --generate-hashes -o requirements.txt
```

To update dependencies, run with `-U`

```bash
python -m piptools compile -U --generate-hashes -o requirements-310.txt
```

More details [here](https://github.com/jazzband/pip-tools)