ancpBIDS is a modular Python library for reading, querying, validating, and writing BIDS datasets. Its architecture is designed for extensibility and maintainability.

Key Features

• BIDS Dataset Loading
  Load BIDS datasets of any size or complexity, with support for multiple BIDS schema versions.

• Flexible Query Engine
  Query files, folders, and metadata using a powerful, Pythonic API. Supports entity-based, scope-based, and custom queries.

• Validation
  Validate datasets against the BIDS specification and custom rules using a plugin-based validation system.

• Writing and Derivatives
  Write and update BIDS datasets, including support for creating and saving BIDS derivatives.

• Lazy Loading
  Efficiently handle large datasets with optional lazy loading, reducing memory usage and speeding up initial access.

• Plugin Architecture
  Extend or customize core functionality (validation, file handling, schema, etc.) via a robust plugin system.

• PyBIDS Compatibility Layer
  Drop-in compatibility for many pybids API calls, easing migration from or integration with existing codebases.

• Synthetic and Real Data Support
  Works with both synthetic test datasets and real-world BIDS datasets.

• CI/CD Ready
  Includes a comprehensive suite of automated and manual tests, with synthetic datasets for reproducibility.

• Extensible and Versioned Schema
  Supports multiple BIDS schema versions and allows for easy extension as the BIDS standard evolves.

Architecture

• Core Models:
  The in-memory graph is hand-maintained in ancpbids/model_base.py. Versioned enums are loaded at runtime from official BIDS schema.json files vendored in ancpbids/schema/versions/.

• Plugin System:
  The extension mechanism (see ancpbids/plugin.py) allows for dynamic extension of core functionality. Plugins can hook into schema modification, dataset processing, file handling, writing, and validation. Graph methods (query, get_schema, …) live on the model classes; SchemaPlugin remains an extension point.

• Query Engine:
  The query logic is implemented in ancpbids/query.py, providing flexible access to dataset contents and metadata.

• Compatibility Layer:
  ancpbids/pybids_compat.py provides compatibility with the pybids API for easier migration and integration.

• Utilities:
  Helper functions and utilities are in ancpbids/utils.py.

• Testing:
  The tests/ directory is organized into auto (CI-safe) and manual (non-deterministic or performance) tests, with synthetic datasets under tests/data/.

Plugin and mixin system

Extensibility comes in two shapes:

• Plugins — hook into load / write / validate / schema / file I/O (execute methods).
• Mixins — add methods to a host class such as BIDSLayout via @mixin(target=...).

Built-in plugins/mixins are registered the same way: decorated with @hook(ranking=0, system=True) / @mixin(...) and listed under ancpbids.plugins / ancpbids.mixins in this project's pyproject.toml. Third-party packages add their own entries to those groups. Hooks are lifecycle contributors (execute); mixins add methods to host classes.

Registering an external plugin

1. Decorate a plugin subclass:

   from ancpbids.plugin import ValidationPlugin, hook
   
   @hook(ranking=1000)
   class SiteRulesPlugin(ValidationPlugin):
       def execute(self, dataset, report: ValidationPlugin.ValidationReport):
           pass

2. In your package’s pyproject.toml:

   [project.entry-points."ancpbids.plugins"]
   site_rules = "lab_bids_extensions.validation:SiteRulesPlugin"

3. Install alongside ancpBIDS; importing ancpbids loads the plugin.

Registering an external mixin

1. Decorate a mixin with a target (live class or "module:Class" string):

   from ancpbids import BIDSLayout
   from ancpbids.plugin import mixin
   
   @mixin(target=BIDSLayout, ranking=1000)
   class MyExportMixin:
       def to_custom(self):
           ...

2. Advertise under ancpbids.mixins:

   [project.entry-points."ancpbids.mixins"]
   my_export = "lab_bids_extensions.exports:MyExportMixin"

Built-in DataFrameMixin lives in ancpbids.mixins.mixin_dataframe, uses @mixin(target=BIDSLayout, ranking=0), and is listed as to_df under the ancpbids.mixins entry-point group in this project's pyproject.toml.

Full guide: docs/source/plugins.rst.

Versioning and Schema Evolution

• The codebase supports multiple BIDS schema versions via vendored schema.json files.
• The schema is loaded dynamically based on the dataset version, allowing for forward compatibility.

Testing and CI

• Unit Tests:
  Located in tests/auto/, these are run automatically in CI.
• Manual/Performance Tests:
  Located in tests/manual/, these are for benchmarking or non-deterministic checks.
• Synthetic Data:
  All tests use synthetic datasets in tests/data/ to ensure reproducibility.

Developer Guidelines

• Extending the Model:
  Add a new ancpbids/schema/versions/schema_v<version>.json (see Model Generation Utility). Type stubs and model_latest update from the vendored JSON files.
• Adding Plugins:
  Follow the plugin system described above (including external entry points).
• Testing:
  Add new tests to tests/auto/ for CI-safe code, and to tests/manual/ for performance or integration tests.
• Documentation:
  Update README.md and docstrings for any new features or changes.

Code Quality

• The codebase uses type hints and docstrings for clarity.
• Contributions should follow PEP8 and include tests and documentation.

Model Generation Utility

The in-memory graph (ancpbids/model_base.py) is hand-maintained. tools/generatemodel.py fetches an official BIDS schema.json into ancpbids/schema/versions/ and writes version-specific type stubs under ancpbids/schema/stubs/ (v1_X_Y.pyi) so IDEs can see enum literals such as SuffixEnum.bold. Enums are still built from JSON at runtime.

Usage:

uv run --with requests python tools/generatemodel.py [--schema-version <version>]
uv run python tools/generatemodel.py --stubs-only

• If --schema-version is omitted, the latest available schema version is used.
• --stubs-only regenerates stubs from JSON files already in ancpbids/schema/versions/.
• Output: ancpbids/schema/versions/schema_v<version>.json, ancpbids/schema/stubs/v1_X_Y.pyi, and ancpbids/schema/stubs/aliases.pyi.

Further Reading

• BIDS Specification
• ancpBIDS Documentation