# The TaskFlow API — Apache Airflow: Orchestrate Data Pipelines

Source: https://www.geekswithgeeks.com/en/airflow/dag-taskflow

> Write DAGs with @dag and @task so Python functions become tasks and return values become XComs.

## Plain functions as tasks

The **TaskFlow API** lets you write tasks as normal Python functions with the `@task` decorator and wire them by calling one with the output of another. Airflow stores the return value as an **XCom** and infers the dependency, so `load(transform(extract()))` creates the chain extract → transform → load. It is concise and the recommended style for Python-based tasks.

## A small ETL with TaskFlow

The data is hard-coded to keep the example self-contained. In a real pipeline `extract` would call an API or database, and only small values would pass between tasks. I ran it with `airflow dags test orders_etl 2026-10-01` on Airflow 3.0.6; the load task printed the total, 120 + 80 + 200 = 400.

```python
from datetime import datetime

from airflow.sdk import dag, task


@dag(
    dag_id="orders_etl",
    start_date=datetime(2026, 9, 1),
    schedule="@daily",
    catchup=False,
    default_args={"retries": 2},
    tags=["demo"],
)
def orders_etl():
    @task
    def extract() -> list[dict]:
        return [{"id": 1, "amount": 120}, {"id": 2, "amount": 80}, {"id": 3, "amount": 200}]

    @task
    def transform(rows: list[dict]) -> int:
        return sum(r["amount"] for r in rows)

    @task
    def load(total: int) -> None:
        print(f"Total revenue loaded: {total}")

    load(transform(extract()))


orders_etl()
```

Output:

```
Total revenue loaded: 400
```

## Type-hint your task functions

Return type hints document what flows between tasks and help catch mistakes early. Keep the values small and serialisable (numbers, strings, small lists and dicts).

**Quiz:** In TaskFlow, how does data pass from one @task to the next?

- [ ] It cannot pass data
- [ ] Through a global variable
- [ ] Through email
- [x] As the return value, stored as an XCom

*Answer:* As the return value, stored as an XCom. Return values become XComs and Airflow wires the dependency automatically.