Add docstring to custom_data hook.

Author: T4rk1n

dash/_callback_context.py

@@ -307,6 +307,9 @@ def origin(self):
     @property
     @has_context
     def custom_data(self):
+        """
+        Custom data set by hooks.custom_data.
+        """
         return _get_from_context("custom_data", {})
 
 

dash/_hooks.py

@@ -192,8 +192,17 @@ def wrap(func):
 
         return wrap
 
-    def custom_data(self, namespace, priority: _t.Optional[int] = None, final=False):
-        def wrap(func):
+    def custom_data(
+        self, namespace: str, priority: _t.Optional[int] = None, final=False
+    ):
+        """
+        Add data to the callback_context.custom_data property under the namespace.
+
+        The hook function takes the current context_value and before the ctx is set
+        and has access to the flask request context.
+        """
+
+        def wrap(func: _t.Callable[[_t.Dict], _t.Any]):
             self.add_hook(
                 "custom_data",
                 func,