Implementation:Apache Airflow DagBag Loader

Knowledge Sources	Apache Airflow
Domains	Testing, DAG_Processing
Last Updated	2026-02-08 00:00 GMT

Overview

Concrete tool for loading and validating DAG files provided by the Airflow DagBag class.

Description

The DagBag class loads DAGs from a specified folder by importing Python files, extracting DAG objects, and tracking import errors. It supports safe mode (only parsing files that contain "DAG" or "airflow" strings), example DAG inclusion, and pool validation. DagBag is used both for local testing and by the DagFileProcessorManager for production DAG discovery.

Usage

Use DagBag directly in tests or scripts to validate DAG files. The airflow dags test CLI command internally uses DagBag for DAG loading before executing a test run.

Code Reference

Source Location

Repository: Apache Airflow
File: airflow-core/src/airflow/dag_processing/dagbag.py
Lines: L162-600

Signature

class DagBag(LoggingMixin):
    def __init__(
        self,
        dag_folder: str | Path | None = None,
        include_examples: bool | ArgNotSet = NOTSET,
        safe_mode: bool | ArgNotSet = NOTSET,
        load_op_links: bool = True,
        collect_dags: bool = True,
        known_pools: set[str] | None = None,
        bundle_path: Path | None = None,
        bundle_name: str | None = None,
    ):
        ...

Import

from airflow.dag_processing.dagbag import DagBag

I/O Contract

Inputs

Name	Type	Required	Description
dag_folder	str or Path or None	No	Path to DAGs directory (defaults to config)
include_examples	bool	No	Include built-in example DAGs
safe_mode	bool	No	Only parse files containing "DAG" or "airflow"
collect_dags	bool	No	Auto-collect DAGs on init (default True)
known_pools	set[str] or None	No	Set of valid pool names for validation

Outputs

Name	Type	Description
dags	dict[str, DAG]	Successfully loaded DAGs keyed by dag_id
import_errors	dict[str, str]	Files with errors keyed by file path
dag_ids	set[str]	Set of all discovered dag_ids

Usage Examples

Validate DAGs in Tests

from airflow.dag_processing.dagbag import DagBag

def test_no_import_errors():
    dagbag = DagBag(dag_folder="/path/to/dags", include_examples=False)
    assert len(dagbag.import_errors) == 0, f"Errors: {dagbag.import_errors}"

def test_dag_loaded():
    dagbag = DagBag(dag_folder="/path/to/dags")
    dag = dagbag.dags.get("my_dag_id")
    assert dag is not None
    assert len(dag.tasks) > 0

Related Pages

Implements Principle

Principle:Apache_Airflow_Local_Testing

Requires Environment

Environment:Apache_Airflow_Python_Runtime_Environment

Uses Heuristic

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