feat: add assets mixin

Author: gadomski

pyproject.toml

@@ -23,10 +23,7 @@ classifiers = [
     "Programming Language :: Python :: 3.13",
 ]
 requires-python = ">=3.10"
-dependencies = [
-    "python-dateutil>=2.9.0.post0",
-    "typing-extensions>=4.12.2",
-]
+dependencies = ["python-dateutil>=2.9.0.post0", "typing-extensions>=4.12.2"]
 
 [project.optional-dependencies]
 validate = ["jsonschema>=4.23.0", "referencing>=0.36.2"]
@@ -38,6 +35,7 @@ dev = [
     "pytest>=8.3.4",
     "ruff>=0.9.6",
     "types-jsonschema>=4.23.0.20241208",
+    "types-python-dateutil>=2.9.0.20241206",
 ]
 bench = ["asv>=0.6.4"]
 docs = ["mike>=2.1.3", "mkdocs-material>=9.6.3", "mkdocstrings-python>=1.14.6"]

src/pystac/asset.py

@@ -75,3 +75,12 @@ def to_dict(self) -> dict[str, Any]:
         d = {"href": self.href}
         d.update(super().to_dict())
         return d
+
+
+class AssetsMixin:
+    """A mixin for things that have assets (Collections and Items)"""
+
+    assets: dict[str, Asset]
+
+    def add_asset(self, key: str, asset: Asset) -> None:
+        raise NotImplementedError

src/pystac/item.py

@@ -5,14 +5,14 @@
 import warnings
 from typing import Any, Sequence
 
-from .asset import Asset
+from .asset import Asset, AssetsMixin
 from .constants import ITEM_TYPE
 from .errors import StacWarning
 from .link import Link
 from .stac_object import STACObject
 
 
-class Item(STACObject):
+class Item(STACObject, AssetsMixin):
     """An Item is a GeoJSON Feature augmented with foreign members relevant to a
     STAC object.
 

src/pystac/stac_object.py

@@ -78,7 +78,7 @@ def from_file(
 
     @classmethod
     def from_dict(
-        cls: type[STACObject],
+        cls: type[Self],
         d: dict[str, Any],
         *,
         href: str | None = None,
@@ -87,7 +87,7 @@ def from_dict(
         preserve_dict: bool = True,  # TODO deprecation warning
         reader: Read | None = None,
         writer: Write | None = None,
-    ) -> STACObject:
+    ) -> Self:
         """Creates a STAC object from a dictionary.
 
         If you already know what type of STAC object your dictionary represents,
@@ -112,17 +112,24 @@ def from_dict(
             if type_value == CATALOG_TYPE:
                 from .catalog import Catalog
 
-                return Catalog(**d, href=href, reader=reader, writer=writer)
+                stac_object: STACObject = Catalog(
+                    **d, href=href, reader=reader, writer=writer
+                )
             elif type_value == COLLECTION_TYPE:
                 from .collection import Collection
 
-                return Collection(**d, href=href, reader=reader, writer=writer)
+                stac_object = Collection(**d, href=href, reader=reader, writer=writer)
             elif type_value == ITEM_TYPE:
                 from .item import Item
 
-                return Item(**d, href=href, reader=reader, writer=writer)
+                stac_object = Item(**d, href=href, reader=reader, writer=writer)
             else:
                 raise StacError(f"unknown type field: {type_value}")
+
+            if isinstance(stac_object, cls):
+                return stac_object
+            else:
+                raise PystacError(f"Expected {cls} but got a {type(stac_object)}")
         else:
             raise StacError("missing type field on dictionary")
 
@@ -140,6 +147,8 @@ def __init__(
         """Creates a new STAC object."""
         from .extensions import Extensions
 
+        super().__init__()
+
         self.id: str = id
         """The object's id."""
 

tests/v1/utils.py

@@ -164,7 +164,7 @@ def all_test_catalogs() -> list[Catalog]:
             TestCases.case_4(),
             TestCases.case_5(),
             TestCases.case_7(),
-            TestCases.case_8(),
+            TestCases.case_8(),  # type: ignore
         ]
 
     @staticmethod