changelog for prevent_initial_call fix, and black

Author: alexcjohnson

CHANGELOG.md

@@ -2,6 +2,10 @@
 All notable changes to `dash` will be documented in this file.
 This project adheres to [Semantic Versioning](https://semver.org/).
 
+## [UNRELEASED]
+### Fixed
+- [#1384](https://github.com/plotly/dash/pull/1384) Fixed a bug introduced by [#1180](https://github.com/plotly/dash/pull/1180) breaking use of `prevent_initial_call` as a positional arg in callback definitions
+
 ## [1.15.0] - 2020-08-25
 ### Added
 - [#1355](https://github.com/plotly/dash/pull/1355) Removed redundant log message and consolidated logger initialization. You can now control the log level - for example suppress informational messages from Dash with `app.logger.setLevel(logging.WARNING)`.

tests/integration/callbacks/test_prevent_initial.py

@@ -339,11 +339,7 @@ def test_cbpi004_positional_arg(dash_duo):
     app = dash.Dash(__name__)
     app.layout = html.Div([html.Button("click", id="btn"), html.Div(id="out")])
 
-    @app.callback(
-        Output("out", "children"),
-        Input("btn", "n_clicks"),
-        True
-    )
+    @app.callback(Output("out", "children"), Input("btn", "n_clicks"), True)
     def f(n):
         return n
 

tests/integration/callbacks/test_validation.py

@@ -207,16 +207,15 @@ def test_cbva005_tuple_args(dash_duo):
     )
 
     @app.callback(
-        Output("out1", "children"),
-        (Input("in1", "children"), Input("in2", "children"))
+        Output("out1", "children"), (Input("in1", "children"), Input("in2", "children"))
     )
     def f(i1, i2):
         return "1: " + i1 + i2
 
     @app.callback(
         (Output("out2", "children"),),
         Input("in1", "children"),
-        (State("in2", "children"),)
+        (State("in2", "children"),),
     )
     def g(i1, i2):
         return ("2: " + i1 + i2,)