Allow to pass functions to PythonNode(hash=...).

docs/source/changes.md

@@ -24,9 +24,10 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - {pull}`402` replaces ABCs with protocols allowing for more flexibility for users
   implementing their own nodes.
 - {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.
+- {pull}`406` allows to match function returns to node annotations with prefix trees.
+- {pull}`408` removes `.value` from `Node` protocol.
+- {pull}`409` make `.from_annot` an optional feature of nodes.
+- {pull}`410` allows to pass functions to `PythonNode(hash=...)`.
 
 ## 0.3.2 - 2023-06-07
 

src/_pytask/nodes.py

@@ -174,7 +174,7 @@ class PythonNode(Node):
     """Name of the node."""
     value: Any = None
     """Value of the node."""
-    hash: bool = False  # noqa: A003
+    hash: bool | Callable[[Any], bool] = False  # noqa: A003
     """Whether the value should be hashed to determine the state."""
 
     def load(self) -> Any:
@@ -206,6 +206,8 @@ def state(self) -> str | None:
         If ``hash = False``, the function returns ``"0"``, a constant hash value, so the
         :class:`PythonNode` is ignored when checking for a changed state of the task.
 
+        If ``hash`` is a callable, then use this function to calculate a hash.
+
         If ``hash = True``, :func:`hash` is used for all types except strings.
 
         The hash for strings is calculated using hashlib because ``hash("asd")`` returns
@@ -214,6 +216,8 @@ def state(self) -> str | None:
 
         """
         if self.hash:
+            if callable(self.hash):
+                return str(self.hash(self.value))
             if isinstance(self.value, str):
                 return str(hashlib.sha256(self.value.encode()).hexdigest())
             return str(hash(self.value))

tests/test_nodes.py

@@ -4,6 +4,7 @@
 from pathlib import Path
 
 import pytest
+from _pytask.nodes import PythonNode
 from _pytask.shared import reduce_node_name
 from pytask import PathNode
 
@@ -35,3 +36,20 @@ def test_reduce_node_name(node, paths, expectation, expected):
     with expectation:
         result = reduce_node_name(node, paths)
         assert result == expected
+
+
+@pytest.mark.unit()
+@pytest.mark.parametrize(
+    ("value", "hash_", "expected"),
+    [
+        (0, False, "0"),
+        (0, True, "0"),
+        (0, lambda x: 1, "1"),  # noqa: ARG005
+        ("0", False, "0"),
+        ("0", True, "5feceb66ffc86f38d952786c6d696c79c2dbc239dd4e91b46729d73a27fb57e9"),
+    ],
+)
+def test_hash_of_python_node(value, hash_, expected):
+    node = PythonNode(name="test", value=value, hash=hash_)
+    state = node.state()
+    assert state == expected