Fix type annotation for hash function. (#655)

Author: tobiasraabe

docs/source/changes.md

@@ -11,6 +11,8 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - {pull}`640` stops the live display when an exception happened during the execution.
 - {pull}`646` adds a `.gitignore` to the `.pytask/` folder to exclude it from version
   control.
+- {pull}`656` fixes the return type of the hash function for {class}`PythonNode`s.
+  Thanks to {user}`axtimhaus` for reporting the issue.
 
 ## 0.5.1 - 2024-07-20
 

docs/source/how_to_guides/hashing_inputs_of_tasks.md

@@ -72,7 +72,8 @@ $ pip install deepdiff
 $ conda install deepdiff
 ```
 
-Then, create the hash function and pass it to the node.
+Then, create the hash function and pass it to the node. Make sure it returns either an
+integer or a string.
 
 `````{tab-set}
 

docs_src/how_to_guides/hashing_inputs_of_tasks_example_3_py310.py

@@ -9,7 +9,7 @@
 from pytask import PythonNode
 
 
-def calculate_hash(x: Any) -> str:
+def calculate_hash(x: Any) -> int | str:
     return DeepHash(x)[x]
 
 

src/_pytask/nodes.py

@@ -216,7 +216,7 @@ class PythonNode(PNode):
         Whether the value should be hashed to determine the state. Use ``True`` for
         objects that are hashable like strings and tuples. For dictionaries and other
         non-hashable objects, you need to provide a function that can hash these
-        objects.
+        objects. The function should return either an integer or a string.
     node_info
         The infos acquired while collecting the node.
 
@@ -235,7 +235,7 @@ class PythonNode(PNode):
 
     name: str = ""
     value: Any | NoDefault = no_default
-    hash: bool | Callable[[Any], bool] = False
+    hash: bool | Callable[[Any], int | str] = False
     node_info: NodeInfo | None = None
 
     @property
@@ -269,7 +269,8 @@ 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`` is a callable, then use this function to calculate a hash expecting
+        an integer or string.
 
         If ``hash = True``, the builtin ``hash()`` function (`link
         <https://docs.python.org/3.11/library/functions.html?highlight=hash#hash>`_) is