Merge pull request #2027 from plotly/err-message

provide simple example of the error

Author: chriddyp

CHANGELOG.md

@@ -28,6 +28,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 - [#1751](https://github.com/plotly/dash/pull/1751) Rename `app.run_server` to `app.run` while preserving `app.run_server` for backwards compatibility.
 
+- [#2027](https://github.com/plotly/dash/pull/1751) Improve the error message when a user doesn't wrap children in a list
 
 ### Updated
 - [#2016](https://github.com/plotly/dash/pull/2016) Widespread dependency upgrades

dash/development/base_component.py

@@ -136,8 +136,9 @@ def __init__(self, **kwargs):
                 raise TypeError(
                     error_string_prefix
                     + " detected a Component for a prop other than `children`\n"
+                    + f"Prop {k} has value {v!r}\n\n"
                     + "Did you forget to wrap multiple `children` in an array?\n"
-                    + f"Prop {k} has value {v!r}\n"
+                    + "For example, it must be html.Div([\"a\", \"b\", \"c\"]) not html.Div(\"a\", \"b\", \"c\")\n"
                 )
 
             if k == "id":