adata.extensions module

[katosh]

Add anndata.extensions module for unified extension API

This PR extends scverse#2236 by adding a public anndata.extensions module that consolidates extension points for external packages.

Live demo: Visual test page (Test 20 shows the unified accessor + section pattern)

Motivation

With the HTML repr system (scverse#2236) introducing register_formatter, TypeFormatter, and SectionFormatter, and the recent addition of register_anndata_namespace (scverse#1870), anndata now has multiple extension mechanisms. However, they're scattered across different locations:

Extension Type	Current Location	Public?
Accessors	anndata.register_anndata_namespace	✅
HTML formatters	anndata._repr.*	❌
I/O handlers	anndata._io.specs._REGISTRY	❌

This follows patterns established by pandas (pd.api.extensions) and xarray for providing a stable extension API.

Changes

1. New anndata/extensions.py module that re-exports:

   • register_anndata_namespace (accessors)
   • register_formatter, TypeFormatter, SectionFormatter (HTML formatters)
   • FormattedOutput, FormattedEntry, FormatterContext
   • formatter_registry
   • extract_uns_type_hint, UNS_TYPE_HINT_KEY

2. Unified accessor + section visualization: Accessors can define a _repr_section_ method to automatically get a section in the HTML repr - no separate SectionFormatter registration needed

3. Updated tests and examples to import from anndata.extensions

4. Updated docstrings to point users to the public API

Usage

Unified accessor with visualization (new!):

from anndata.extensions import (
    register_anndata_namespace,
    FormattedEntry,
    FormattedOutput,
)

@register_anndata_namespace("spatial")
class SpatialAccessor:
    # Optional: configure section in HTML output
    section_after = "obsm"  # Position after obsm section
    section_display_name = "spatial"  # Display name (defaults to accessor name)
    section_tooltip = "Spatial data"  # Hover tooltip
    section_doc_url = "https://spatialdata.readthedocs.io/"  # Doc link icon

    def __init__(self, adata: ad.AnnData):
        self._adata = adata

    @property
    def images(self):
        return self._adata.uns.get("spatial_images", {})

    def add_image(self, key, image):
        if "spatial_images" not in self._adata.uns:
            self._adata.uns["spatial_images"] = {}
        self._adata.uns["spatial_images"][key] = image

    def _repr_section_(self, context) -> list[FormattedEntry] | None:
        """Return entries for HTML repr, or None to hide section."""
        if not self.images:
            return None
        return [
            FormattedEntry(
                key=k,
                output=FormattedOutput(type_name=f"Image {v.shape}"),
            )
            for k, v in self.images.items()
        ]

# Usage:
adata.spatial.add_image("hires", image_array)
adata._repr_html_()  # Shows "spatial" section automatically!

Separate formatter registration (still supported):

from anndata.extensions import (
    register_formatter,
    SectionFormatter,
    FormattedEntry,
    FormattedOutput,
)

@register_formatter
class ObstSectionFormatter(SectionFormatter):
    section_name = "obst"
    after_section = "obsm"

    def should_show(self, obj):
        return hasattr(obj, "obst") and len(obj.obst) > 0

    def get_entries(self, obj, context):
        return [
            FormattedEntry(
                key=k,
                output=FormattedOutput(type_name=f"Tree ({v.n_nodes} nodes)"),
            )
            for k, v in obj.obst.items()
        ]

Future direction: Unified extension ecosystem

This aligns with the anndata roadmap (scverse#448) and ongoing discussions about extensibility. anndata already has an internal IORegistry (anndata._io.specs.registry) that handles serialization registration with register_read and register_write methods. Making this public would complete the extension story:

# Future possibility
from anndata.extensions import (
    # Accessors (already available)
    register_anndata_namespace,
    # HTML visualization (this PR)
    register_formatter,
    TypeFormatter,
    SectionFormatter,
    # I/O serialization (future - exposing existing IORegistry)
    register_io_handler,
    IOSpec,
)

This would address:

• Custom dtype handling (Handle new zarr dtypes (both custom and datetime) scverse/anndata#2238) - packages could register serializers for new zarr dtypes
• TreeData/SpatialData/MuData integration - register both visualization and serialization for custom sections
• The pattern established by pandas (pd.api.extensions) and xarray for stable extension APIs

The existing IORegistry infrastructure is already well-designed with support for:

• Type-based dispatch (register_write(dest_type, src_type, spec))
• Version-aware specs (IOSpec("dataframe", "0.2.0"))
• Read/write/read_partial methods

Exposing it through anndata.extensions would provide a stable public API without changing the internal implementation.

Visual Test

The visual test page includes 20 test cases demonstrating various features. Test 20 specifically shows the unified accessor + section pattern with a spatial_demo accessor.

Source: repr_html_visual_test.html gist

Checklist

• Tests pass
• Examples updated to use new import location
• Docstrings updated with note about public API
• Visual test includes unified accessor + section example (Test 20)

[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/anndata/extensions.py (1)

1-70: Public re-export module matches the PR objective; examples are clear.
One consideration: importing anndata.extensions will eagerly import anndata._repr; if import-time becomes a concern, consider lazy re-exports (module __getattr__) later.

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 7c7058b and 6383dd1.

📒 Files selected for processing (4)

• src/anndata/_repr/__init__.py (4 hunks)
• src/anndata/extensions.py (1 hunks)
• tests/test_repr_html.py (12 hunks)
• tests/visual_inspect_repr_html.py (3 hunks)

🧰 Additional context used

🧬 Code graph analysis (2)

tests/test_repr_html.py (1)

src/anndata/_repr/registry.py (3)

• FormatterContext (102-141)
• SectionFormatter (202-277)
• TypeFormatter (144-199)

src/anndata/extensions.py (2)

src/anndata/_core/extensions.py (1)

• register_anndata_namespace (146-237)

src/anndata/_repr/registry.py (8)

• FormattedEntry (88-98)
• FormattedOutput (56-84)
• FormatterContext (102-141)
• FormatterRegistry (339-417)
• SectionFormatter (202-277)
• TypeFormatter (144-199)
• register_formatter (523-551)
• extract_uns_type_hint (432-520)

🪛 Ruff (0.14.8)

src/anndata/extensions.py

95-110: __all__ is not sorted

Apply an isort-style sorting to __all__

(RUF022)

🔇 Additional comments (10)

src/anndata/_repr/__init__.py (3)

13-24: Doc note correctly steers users to the new public extension API.
This aligns the docs with the PR goal without affecting runtime behavior.

---

39-62: Example import paths updated to anndata.extensions (good).
Keeps the extensibility guidance on the supported public surface.

---

99-105: SectionFormatter example updated to public imports (good).

tests/visual_inspect_repr_html.py (3)

24-29: Import migration to anndata.extensions is consistent with the new public API.

---

43-49: Optional-dependency block correctly imports extension symbols from the public module.

---

241-247: MuData block uses the public extension import surface (good).

tests/test_repr_html.py (4)

692-693: LGTM: tests now consume the public formatter_registry export.

---

699-705: LGTM: registry/type context symbols imported from anndata.extensions.

---

742-743: LGTM: public imports used for fallback behavior test.

---

1707-1713: LGTM: type-hint formatter test now uses the public extension API.

[coderabbitai]

⚠️ Potential issue | 🟡 Minor

Fix Ruff RUF022 on __all__ (either sort, or explicitly ignore).
Given other modules intentionally group exports by category, adding the same # noqa: RUF022 pattern here seems simplest.

-__all__ = [
+__all__ = [  # noqa: RUF022  # organized by category, not alphabetically
     # Accessor registration
     "register_anndata_namespace",
     # HTML formatter registration
     "register_formatter",
     "TypeFormatter",
     "SectionFormatter",
     "FormattedOutput",
     "FormattedEntry",
     "FormatterContext",
     "FormatterRegistry",
     "formatter_registry",
     # Type hint utilities
     "extract_uns_type_hint",
     "UNS_TYPE_HINT_KEY",
 ]

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	__all__ = [
	# Accessor registration
	"register_anndata_namespace",
	# HTML formatter registration
	"register_formatter",
	"TypeFormatter",
	"SectionFormatter",
	"FormattedOutput",
	"FormattedEntry",
	"FormatterContext",
	"FormatterRegistry",
	"formatter_registry",
	# Type hint utilities
	"extract_uns_type_hint",
	"UNS_TYPE_HINT_KEY",
	]
	__all__ = [ # noqa: RUF022 # organized by category, not alphabetically
	# Accessor registration
	"register_anndata_namespace",
	# HTML formatter registration
	"register_formatter",
	"TypeFormatter",
	"SectionFormatter",
	"FormattedOutput",
	"FormattedEntry",
	"FormatterContext",
	"FormatterRegistry",
	"formatter_registry",
	# Type hint utilities
	"extract_uns_type_hint",
	"UNS_TYPE_HINT_KEY",
	]

🧰 Tools

🪛 Ruff (0.14.8)

95-110: __all__ is not sorted

Apply an isort-style sorting to __all__

(RUF022)

🤖 Prompt for AI Agents

In src/anndata/extensions.py around lines 95 to 110, the grouped __all__ export
list triggers Ruff RUF022 (unsorted __all__); to silence it without reordering,
append an explicit noqa for RUF022 to the __all__ assignment (e.g. add "# noqa:
RUF022" on the __all__ line or the closing bracket line) so the linter ignores
the unsorted export list while preserving the intentional grouping.

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