Add .ext to stac objects (#1717)

Author: jsignell

src/pystac/asset.py

@@ -18,6 +18,7 @@
 from .writer import Writer
 
 if TYPE_CHECKING:
+    from .extensions.ext import AssetExt
     from .stac_object import STACObject
 
 
@@ -132,6 +133,18 @@ def to_dict(self) -> dict[str, Any]:
         data = super().to_dict()
         return {"href": self.href, **data}
 
+    @property
+    def ext(self) -> AssetExt:
+        """Accessor for extension classes on this asset
+
+        Example::
+
+            asset.ext.proj.code = "EPSG:4326"
+        """
+        from pystac.extensions.ext import AssetExt
+
+        return AssetExt(stac_object=self)
+
 
 class Assets(Protocol):
     assets: dict[str, Asset]

src/pystac/catalog.py

@@ -3,7 +3,7 @@
 import copy
 import warnings
 from enum import StrEnum
-from typing import Any, ClassVar, override
+from typing import TYPE_CHECKING, Any, ClassVar, override
 
 from typing_extensions import deprecated
 
@@ -13,6 +13,9 @@
 from .link import Link
 from .rel_type import RelType
 
+if TYPE_CHECKING:
+    from .extensions.ext import CatalogExt
+
 
 class Catalog(Container):
     type: ClassVar[STAC_OBJECT_TYPE] = "Catalog"
@@ -83,6 +86,18 @@ def to_dict(
         data["description"] = self.description
         return data
 
+    @property
+    def ext(self) -> CatalogExt:
+        """Accessor for extension classes on this catalog
+
+        Example::
+
+            print(collection.ext.version)
+        """
+        from pystac.extensions.ext import CatalogExt
+
+        return CatalogExt(stac_object=self)
+
 
 @deprecated("CatalogType is deprecated")
 class CatalogType(StrEnum):

src/pystac/collection.py

@@ -26,6 +26,7 @@
 from .utils import to_datetime_str
 
 if TYPE_CHECKING:
+    from .extensions.ext import CollectionExt
     from .item import Item
     from .item_collection import ItemCollection
 
@@ -218,6 +219,18 @@ def update_extent_from_items(self) -> None:
         """
         self.extent = Extent.from_items(self.get_items(recursive=True))
 
+    @property
+    def ext(self) -> CollectionExt:
+        """Accessor for extension classes on this collection
+
+        Example::
+
+            print(collection.ext.xarray)
+        """
+        from pystac.extensions.ext import CollectionExt
+
+        return CollectionExt(stac_object=self)
+
 
 class Extent:
     def __init__(

src/pystac/item.py

@@ -29,6 +29,7 @@
 
 if TYPE_CHECKING:
     from .collection import Collection
+    from .extensions.ext import ItemExt
 
 
 class Item(STACObject, Assets):
@@ -241,6 +242,18 @@ def to_dict(
     def __geo_interface__(self) -> dict[str, Any]:
         return self.to_dict(include_self_link=False)
 
+    @property
+    def ext(self) -> ItemExt:
+        """Accessor for extension classes on this item
+
+        Example::
+
+            item.ext.proj.code = "EPSG:4326"
+        """
+        from pystac.extensions.ext import ItemExt
+
+        return ItemExt(stac_object=self)
+
 
 @final
 class Properties(

src/pystac/link.py

@@ -16,6 +16,7 @@
 
 if TYPE_CHECKING:
     from . import Catalog, Collection, Item
+    from .extensions.ext import LinkExt
     from .stac_object import STACObject
 
 HIERARCHICAL_LINKS = [
@@ -318,3 +319,15 @@ def canonical(
             title=title,
             media_type=MediaType.JSON,
         )
+
+    @property
+    def ext(self) -> LinkExt:
+        """Accessor for extension classes on this link
+
+        Example::
+
+            link.ext.file.size = 8675309
+        """
+        from pystac.extensions.ext import LinkExt
+
+        return LinkExt(stac_object=self)