Make .from_annot an optional feature of nodes.

docs/source/changes.md

@@ -26,6 +26,7 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - {pull}`404` allows to use function returns to define task products.
 - {pull}`405` allows to match function returns to node annotations with prefix trees.
 - {pull}`406` removes `.value` from `Node` protocol.
+- {pull}`407` make `.from_annot` an optional feature of nodes.
 
 ## 0.3.2 - 2023-06-07
 

src/_pytask/collect_utils.py

@@ -601,5 +601,11 @@ def _evolve_instance(x: Any, instance_from_annot: Node | None) -> Any:
     if not instance_from_annot:
         return x
 
-    instance_from_annot.from_annot(x)
+    if not hasattr(instance_from_annot, "from_annot"):
+        raise AttributeError(
+            f"The node {instance_from_annot!r} does not define '.from_annot' which is "
+            f"necessary to complete the node with the value {x!r}."
+        )
+
+    instance_from_annot.from_annot(x)  # type: ignore[attr-defined]
     return instance_from_annot

src/_pytask/node_protocols.py

@@ -37,21 +37,6 @@ def save(self, value: Any) -> Any:
         """Save the value that was returned from a task."""
         ...
 
-    def from_annot(self, value: Any) -> Any:
-        """Complete the node by setting the value from an default argument.
-
-        Use it, if you want to add information on how a node handles an argument while
-        keeping the type of the value unrelated to pytask.
-
-        .. codeblock: python
-
-            def task_example(value: Annotated[Any, PythonNode(hash=True)], produces):
-                ...
-
-
-        """
-        ...
-
 
 @runtime_checkable
 class PPathNode(Node, Protocol):

src/_pytask/nodes.py

@@ -111,7 +111,17 @@ class PathNode(PPathNode):
     """The path to the file."""
 
     def from_annot(self, value: Path) -> None:
-        """Set path and if other attributes are not set, set sensible defaults."""
+        """Set path and if other attributes are not set, set sensible defaults.
+
+        Use it, if you want to control the name of the node.
+
+        .. codeblock: python
+
+            def task_example(value: Annotated[Any, PathNode(name="value")]):
+                ...
+
+
+        """
         if not isinstance(value, Path):
             raise TypeError("'value' must be a 'pathlib.Path'.")
         if not self.name:
@@ -176,7 +186,18 @@ def save(self, value: Any) -> None:
         self.value = value
 
     def from_annot(self, value: Any) -> None:
-        """Set the value from a function annotation."""
+        """Set the value from a function annotation.
+
+        Use it, if you want to add information on how a node handles an argument while
+        keeping the type of the value unrelated to pytask. For example, the node could
+        be hashed.
+
+        .. codeblock: python
+
+            def task_example(value: Annotated[Any, PythonNode(hash=True)]):
+                ...
+
+        """
         self.value = value
 
     def state(self) -> str | None: