Move NOT_DATA to its own module

notebooks/deepdive.ipynb

@@ -22,7 +22,8 @@
     }
    },
    "source": [
-    "import pyiron_workflow as pwf"
+    "import pyiron_workflow as pwf\n",
+    "import pyiron_workflow.data"
    ],
    "outputs": [],
    "execution_count": 81
@@ -293,7 +294,7 @@
     "    _output_labels = (\"plus\", \"minus\")\n",
     "\n",
     "    def is_bound(self, n) -> bool:\n",
-    "        if self.outputs.plus.value is not pwf.api.NOT_DATA:\n",
+    "        if self.outputs.plus.value is not pyiron_workflow.data.NOT_DATA:\n",
     "            return self.outputs.plus.value > n and self.outputs.minus.value < n\n",
     "        else:\n",
     "            raise RuntimeError(\"Run the node first\")\n",
@@ -1178,7 +1179,7 @@
    "source": [
     "i2d = pwf.api.inputs_to_dict(\n",
     "    input_specification={\n",
-    "        \"x\": (None, pwf.api.NOT_DATA),\n",
+    "        \"x\": (None, pyiron_workflow.data.NOT_DATA),\n",
     "        \"y\": (int, 42)\n",
     "    }\n",
     ")\n",
@@ -1628,7 +1629,7 @@
      "start_time": "2025-08-13T22:35:56.546690Z"
     }
    },
-   "source": "assert(pwf.std.UserInput().inputs.user_input.value is pwf.api.NOT_DATA)",
+   "source": "assert(pwf.std.UserInput().inputs.user_input.value is pyiron_workflow.data.NOT_DATA)",
    "outputs": [],
    "execution_count": 120
   },

pyiron_workflow/api.py

@@ -5,7 +5,7 @@
 """
 
 # Node developer entry points
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.executors import CloudpickleProcessPoolExecutor, NodeSlurmExecutor
 from pyiron_workflow.find import (
     find_nodes as _find_nodes,  # Not formally in API -- don't rely on interface

pyiron_workflow/channels.py

@@ -12,8 +12,7 @@
 import typing
 from abc import ABC, abstractmethod
 
-from pyiron_snippets.singleton import Singleton
-
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.mixin.display_state import HasStateDisplay
 from pyiron_workflow.mixin.has_interface_mixins import HasChannel, HasLabel
 from pyiron_workflow.type_hinting import (
@@ -304,29 +303,6 @@ class OutputChannel(Channel[InputType], ABC):
     """Mixin for output channels."""
 
 
-class NotData(metaclass=Singleton):
-    """
-    This class exists purely to initialize data channel values where no default value
-    is provided; it lets the channel know that it has _no data in it_ and thus should
-    not identify as ready.
-    """
-
-    @classmethod
-    def __repr__(cls):
-        # We use the class directly (not instances of it) where there is not yet data
-        # So give it a decent repr, even as just a class
-        return "NOT_DATA"
-
-    def __reduce__(self):
-        return "NOT_DATA"
-
-    def __bool__(self):
-        return False
-
-
-NOT_DATA = NotData()
-
-
 class DataChannel(FlavorChannel["DataChannel"], typing.Generic[ReceiverType], ABC):
     """
     Data channels control the flow of data on the graph.

pyiron_workflow/data.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+from pyiron_snippets.singleton import Singleton
+
+
+class NotData(metaclass=Singleton):
+    """
+    This class exists purely to initialize data channel values where no default value
+    is provided; it lets the channel know that it has _no data in it_ and thus should
+    not identify as ready.
+    """
+
+    @classmethod
+    def __repr__(cls):
+        # We use the class directly (not instances of it) where there is not yet data
+        # So give it a decent repr, even as just a class
+        return "NOT_DATA"
+
+    def __reduce__(self):
+        return "NOT_DATA"
+
+    def __bool__(self):
+        return False
+
+
+NOT_DATA = NotData()

pyiron_workflow/draw.py

@@ -10,7 +10,7 @@
 import graphviz
 from pyiron_snippets.colors import SeabornColors
 
-from pyiron_workflow.channels import NotData
+from pyiron_workflow.data import NOT_DATA
 
 if TYPE_CHECKING:
     from pyiron_workflow.channels import Channel as WorkflowChannel  # noqa: F401
@@ -198,7 +198,7 @@ def shape(self) -> str:
 
     @property
     def style(self) -> str:
-        if len(self.channel.connections) == 0 and self.channel.value is NotData():
+        if len(self.channel.connections) == 0 and self.channel.value is NOT_DATA:
             return "bold"
         return "filled"
 

pyiron_workflow/mixin/injection.py

@@ -11,7 +11,8 @@
 import abc
 from typing import TYPE_CHECKING, Any
 
-from pyiron_workflow.channels import NOT_DATA, OutputData
+from pyiron_workflow.channels import OutputData
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.io import GenericOutputs
 from pyiron_workflow.mixin.has_interface_mixins import HasChannel
 

pyiron_workflow/mixin/preview.py

@@ -25,7 +25,7 @@
 
 from pyiron_snippets.dotdict import DotDict
 
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.logging import logger
 from pyiron_workflow.output_parser import ParseOutput
 

pyiron_workflow/nodes/for_loop.py

@@ -10,7 +10,7 @@
 from pandas import DataFrame
 from pyiron_snippets.factory import classfactory
 
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.mixin.run import InterpretableAsExecutor
 from pyiron_workflow.nodes.composite import Composite
 from pyiron_workflow.nodes.static_io import StaticNode

pyiron_workflow/nodes/standard.py

@@ -11,7 +11,8 @@
 from pathlib import Path
 from time import sleep
 
-from pyiron_workflow.channels import NOT_DATA, OutputSignal
+from pyiron_workflow.channels import OutputSignal
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.nodes.function import Function, as_function_node
 
 

pyiron_workflow/nodes/transform.py

@@ -15,7 +15,7 @@
 from pyiron_snippets.factory import classfactory
 
 from pyiron_workflow import identifier
-from pyiron_workflow.channels import NOT_DATA, NotData
+from pyiron_workflow.data import NOT_DATA, NotData
 from pyiron_workflow.nodes.static_io import StaticNode
 
 

tests/cluster/slurm_test.py

@@ -3,13 +3,16 @@
 import time
 
 import pyiron_workflow as pwf
+import pyiron_workflow.data
 from pyiron_workflow.executors.wrapped_executorlib import NodeSlurmExecutor
 
 t_overhead = 2
 t_sleep = 10
 
 
-def state_check(wf, expected_wf, expected_n2, expected_result=pwf.api.NOT_DATA):
+def state_check(
+    wf, expected_wf, expected_n2, expected_result=pyiron_workflow.data.NOT_DATA
+):
     wf_running, n_running, outputs = (
         wf.running,
         wf.n2.running,

tests/integration/test_workflow.py

@@ -9,7 +9,8 @@
 from static import demo_nodes
 
 from pyiron_workflow._tests import ensure_tests_in_python_path
-from pyiron_workflow.channels import NOT_DATA, OutputSignal
+from pyiron_workflow.channels import OutputSignal
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.nodes.composite import FailedChildError
 from pyiron_workflow.nodes.function import Function
 from pyiron_workflow.workflow import Workflow

tests/unit/mixin/test_preview.py

@@ -3,7 +3,7 @@
 
 from pyiron_snippets.factory import classfactory
 
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.logging import logger
 from pyiron_workflow.mixin.preview import ScrapesIO, no_output_validation_warning
 

tests/unit/nodes/test_composite.py

@@ -5,7 +5,7 @@
 from static import demo_nodes
 
 from pyiron_workflow._tests import ensure_tests_in_python_path
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.io import Inputs
 from pyiron_workflow.mixin.injection import OutputsWithInjection
 from pyiron_workflow.nodes.composite import Composite

tests/unit/nodes/test_function.py

@@ -4,7 +4,7 @@
 
 import numpy as np
 
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.node import (
     Node as NonBuiltinTypeHint,
 )

tests/unit/nodes/test_macro.py

@@ -5,6 +5,7 @@
 
 from static import demo_nodes
 
+import pyiron_workflow.data
 from pyiron_workflow import channels
 from pyiron_workflow._tests import ensure_tests_in_python_path
 from pyiron_workflow.mixin import injection
@@ -148,7 +149,7 @@ def test_creation_from_decorator(self):
 
         self.assertIs(
             m.outputs.three__result.value,
-            channels.NOT_DATA,
+            pyiron_workflow.data.NOT_DATA,
             msg="Output should be accessible with the usual naming convention, but we "
             "have not run yet so there shouldn't be any data",
         )
@@ -221,7 +222,7 @@ def test_with_executor(self):
         macro.executor = futures.ProcessPoolExecutor()
 
         self.assertIs(
-            channels.NOT_DATA,
+            pyiron_workflow.data.NOT_DATA,
             macro.outputs.three__result.value,
             msg="Sanity check that test is in right starting condition",
         )
@@ -231,7 +232,7 @@ def test_with_executor(self):
             result, futures.Future, msg="Should be running as a parallel process"
         )
         self.assertIs(
-            channels.NOT_DATA,
+            pyiron_workflow.data.NOT_DATA,
             downstream.outputs.result.value,
             msg="Downstream events should not yet have triggered either, we should wait"
             "for the callback when the result is ready",
@@ -657,7 +658,7 @@ def DoesntAutoloadChildren(self, x):
 
             self.assertIs(
                 DoesntAutoloadChildren().some_child.outputs.x.value,
-                channels.NOT_DATA,
+                pyiron_workflow.data.NOT_DATA,
                 msg="Despite having the same label as a saved node at instantiation time, "
                 "without autoloading children, our macro safely gets a fresh instance. "
                 "Since this is clearly preferable, here we leave autoload to take its "

tests/unit/nodes/test_transform.py

@@ -6,7 +6,7 @@
 
 from pandas import DataFrame
 
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.nodes.function import as_function_node
 from pyiron_workflow.nodes.transform import (
     Transformer,

tests/unit/test_channels.py

@@ -3,7 +3,6 @@
 import unittest
 
 from pyiron_workflow.channels import (
-    NOT_DATA,
     AccumulatingInputSignal,
     BadCallbackError,
     Channel,
@@ -16,6 +15,7 @@
     OutputSignal,
     TooManyConnectionsError,
 )
+from pyiron_workflow.data import NOT_DATA
 
 
 class DummyParent:

tests/unit/test_node.py

@@ -4,10 +4,10 @@
 import bagofholding as boh
 
 from pyiron_workflow.channels import (
-    NOT_DATA,
     InputData,
     InputLockedError,
 )
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.io import Inputs
 from pyiron_workflow.mixin.injection import (
     OutputDataWithInjection,

tests/unit/test_workflow.py

@@ -8,7 +8,7 @@
 from static import demo_nodes
 
 from pyiron_workflow._tests import ensure_tests_in_python_path
-from pyiron_workflow.channels import NOT_DATA
+from pyiron_workflow.data import NOT_DATA
 from pyiron_workflow.storage import TypeNotFoundError, available_backends
 from pyiron_workflow.workflow import NoArgsError, ParentMostError, Workflow