Truncate InvalidCallbackReturnValue size

dash/_validate.py

@@ -2,6 +2,9 @@
 import re
 from textwrap import dedent
 from keyword import iskeyword
+from typing import Any
+from typing_extensions import Final
+
 import flask
 
 from ._grouping import grouping_len, map_grouping
@@ -15,6 +18,8 @@
  clean_property_name,
 )
 
+TRUNCATE_AT: Final[int] = 100
+
 
 def validate_callback(outputs, inputs, state, extra_args, types):
  Input, Output, State = types
@@ -209,11 +214,23 @@ def validate_multi_return(output_lists, output_values, callback_id):
  )
 
 
+def truncate_object(obj: Any, at: int) -> str:
+ """Return a truncated string representation of an object."""
+ obj_stringified = str(obj)
+ size = len(obj_stringified)
+
+ if size <= at:
+ return obj_stringified
+
+ return obj_stringified[:at] + f"... (truncated - {size} characters total)"
+
+
 def fail_callback_output(output_value, output):
  valid_children = (str, int, float, type(None), Component)
  valid_props = (str, int, float, type(None), tuple, MutableSequence)
 
  def _raise_invalid(bad_val, outer_val, path, index=None, toplevel=False):
+ bad_val_stringified = truncate_object(bad_val, TRUNCATE_AT)
  bad_type = type(bad_val).__name__
  outer_id = f"(id={outer_val.id:s})" if getattr(outer_val, "id", False) else ""
  outer_type = type(outer_val).__name__
@@ -244,7 +261,7 @@ def _raise_invalid(bad_val, outer_val, path, index=None, toplevel=False):
 
  {location}
  and has string representation
- `{bad_val}`
+ `{bad_val_stringified}`
 
  In general, Dash properties can only be
  dash components, strings, dictionaries, numbers, None,

tests/integration/devtools/test_devtools_error_handling.py

@@ -1,5 +1,5 @@
 # -*- coding: UTF-8 -*-
-from dash import Dash, Input, Output, html, dcc
+from dash import _validate, Dash, Input, Output, html, dcc
 from dash.exceptions import PreventUpdate
 
 
@@ -260,3 +260,86 @@ def update_outputs(n_clicks):
  dash_duo.wait_for_text_to_equal(dash_duo.devtools_error_count_locator, "1")
  dash_duo.find_element(".test-devtools-error-toggle").click()
  dash_duo.percy_snapshot("devtools - multi output Python exception - open")
+
+
+def test_dveh006_truncate_callback(dash_duo):
+ app = Dash(__name__)
+
+ from dataclasses import dataclass
+ from typing import List, Dict, Any
+
+ @dataclass
+ class GenericItemA:
+ attribute_1: int
+ attribute_2: str
+
+ @dataclass
+ class GenericItemB:
+ key: str
+ value: List[str]
+
+ @dataclass
+ class GenericItemC:
+ identifier: int
+ description: str
+
+ @dataclass
+ class GenericOptions:
+ option_key: str
+ option_value: Any
+
+ @dataclass
+ class GenericDataModel:
+ ItemListA: List[GenericItemA]
+ SingleItemB: GenericItemB
+ NestedItemListC: List[List[GenericItemC]]
+ Options: GenericOptions
+ Metadata: Dict
+ AdditionalInfo: Any
+
+ app.layout = html.P(id="output")
+
+ @app.callback(Output("output", "children"), Input("url", "href"))
+ def get_width(_):
+ item_list_a = [
+ GenericItemA(attribute_1=123, attribute_2="Alpha"),
+ GenericItemA(attribute_1=456, attribute_2="Beta")
+ ]
+
+ single_item_b = GenericItemB(key="Key1", value=["Item1", "Item2"])
+
+ nested_item_list_c = [
+ [GenericItemC(identifier=101, description="Description1")],
+ [GenericItemC(identifier=102, description="Description2")]
+ ]
+
+ generic_options = GenericOptions(option_key="Option1", option_value="Value1")
+
+ generic_metadata = {"meta_key": "meta_value"}
+
+ additional_info = "Generic information"
+
+ # Creating an instance of GenericDataModel
+ generic_data_model = GenericDataModel(
+ ItemListA=item_list_a,
+ SingleItemB=single_item_b,
+ NestedItemListC=nested_item_list_c,
+ Options=generic_options,
+ Metadata=generic_metadata,
+ AdditionalInfo=additional_info
+ )
+
+ return generic_data_model
+
+ dash_duo.start_server(
+ app,
+ debug=True,
+ use_reloader=False,
+ use_debugger=True,
+ dev_tools_hot_reload=False,
+ )
+
+ dash_duo.find_element(".dash-debug-menu").click()
+ dash_duo.wait_for_text_to_equal(dash_duo.devtools_error_count_locator, "1")
+
+ assert len(get_error_html(dash_duo, 0)) == _validate.TRUNCATE_AT