Move NOT_DATA to its own module (#746)

Signed-off-by: liamhuber <[email protected]>

Author: liamhuber

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