Merge pull request #548 from plotly/remove-prevent-update-print

Remove print statement from PreventUpdate handler.

Author: T4rk1n

Diff for: CHANGELOG.md

@@ -2,6 +2,7 @@
 ## Fixed
 - Asset blueprint takes routes prefix into it's static path. [#547](https://github.com/plotly/dash/pull/547)
 - Asset url path no longer strip routes from requests. [#547](https://github.com/plotly/dash/pull/547)
+- Remove print statement from PreventUpdate error handler. [#548](https://github.com/plotly/dash/pull/548)
 
 ## Changed
 - `assets_folder` argument now default to 'assets' [#547](https://github.com/plotly/dash/pull/547)

Diff for: dash/dash.py

@@ -169,10 +169,9 @@ def __init__(
             Compress(self.server)
 
         @self.server.errorhandler(exceptions.PreventUpdate)
-        def _handle_error(error):
+        def _handle_error(_):
             """Handle a halted callback and return an empty 204 response"""
-            print(error, file=sys.stderr)
-            return ('', 204)
+            return '', 204
 
         # static files from the packages
         self.css = Css()