Merge pull request #3127 from 2Ryan09/no-update-is-valid-prop

`NoUpdate` is a Valid Prop

Author: T4rk1n

dash/_callback.py

@@ -42,6 +42,7 @@
 from . import _validate
 from .background_callback.managers import BaseBackgroundCallbackManager
 from ._callback_context import context_value
+from ._no_update import NoUpdate
 
 
 async def _async_invoke_callback(
@@ -58,17 +59,6 @@ def _invoke_callback(func, *args, **kwargs):  # used to mark the frame for the d
     return func(*args, **kwargs)  # %% callback invoked %%
 
 
-class NoUpdate:
-    def to_plotly_json(self):  # pylint: disable=no-self-use
-        return {"_dash_no_update": "_dash_no_update"}
-
-    @staticmethod
-    def is_no_update(obj):
-        return isinstance(obj, NoUpdate) or (
-            isinstance(obj, dict) and obj == {"_dash_no_update": "_dash_no_update"}
-        )
-
-
 GLOBAL_CALLBACK_LIST = []
 GLOBAL_CALLBACK_MAP = {}
 GLOBAL_INLINE_SCRIPTS = []

dash/_no_update.py

@@ -0,0 +1,9 @@
+class NoUpdate:
+    def to_plotly_json(self):  # pylint: disable=no-self-use
+        return {"_dash_no_update": "_dash_no_update"}
+
+    @staticmethod
+    def is_no_update(obj):
+        return isinstance(obj, NoUpdate) or (
+            isinstance(obj, dict) and obj == {"_dash_no_update": "_dash_no_update"}
+        )

dash/_validate.py

@@ -6,6 +6,7 @@
 import flask
 
 from ._grouping import grouping_len, map_grouping
+from ._no_update import NoUpdate
 from .development.base_component import Component
 from . import exceptions
 from ._utils import (
@@ -211,8 +212,8 @@ def validate_multi_return(output_lists, output_values, callback_id):
 
 
 def fail_callback_output(output_value, output):
-    valid_children = (str, int, float, type(None), Component)
-    valid_props = (str, int, float, type(None), tuple, MutableSequence)
+    valid_children = (str, int, float, type(None), Component, NoUpdate)
+    valid_props = (str, int, float, type(None), tuple, MutableSequence, NoUpdate)
 
     def _raise_invalid(bad_val, outer_val, path, index=None, toplevel=False):
         bad_type = type(bad_val).__name__