Merge pull request #3130 from plotly/fix-run-params

Fix run host/port default arguments

Author: T4rk1n

dash/dash.py

@@ -2005,25 +2005,26 @@ def delete_resource(resources):
                         # pylint: disable=protected-access
                         delete_resource(self.css._resources._resources)
 
+    # pylint: disable=too-many-branches
     def run(
         self,
-        host="127.0.0.1",
-        port="8050",
-        proxy=None,
-        debug=None,
+        host: Optional[str] = None,
+        port: Optional[Union[str, int]] = None,
+        proxy: Optional[str] = None,
+        debug: Optional[bool] = None,
         jupyter_mode: Optional[JupyterDisplayMode] = None,
-        jupyter_width="100%",
-        jupyter_height=650,
-        jupyter_server_url=None,
-        dev_tools_ui=None,
-        dev_tools_props_check=None,
-        dev_tools_serve_dev_bundles=None,
-        dev_tools_hot_reload=None,
-        dev_tools_hot_reload_interval=None,
-        dev_tools_hot_reload_watch_interval=None,
-        dev_tools_hot_reload_max_retry=None,
-        dev_tools_silence_routes_logging=None,
-        dev_tools_prune_errors=None,
+        jupyter_width: str = "100%",
+        jupyter_height: int = 650,
+        jupyter_server_url: Optional[str] = None,
+        dev_tools_ui: Optional[bool] = None,
+        dev_tools_props_check: Optional[bool] = None,
+        dev_tools_serve_dev_bundles: Optional[bool] = None,
+        dev_tools_hot_reload: Optional[bool] = None,
+        dev_tools_hot_reload_interval: Optional[int] = None,
+        dev_tools_hot_reload_watch_interval: Optional[int] = None,
+        dev_tools_hot_reload_max_retry: Optional[int] = None,
+        dev_tools_silence_routes_logging: Optional[bool] = None,
+        dev_tools_prune_errors: Optional[bool] = None,
         **flask_run_options,
     ):
         """Start the flask server in local mode, you should not run this on a
@@ -2032,11 +2033,11 @@ def run(
         If a parameter can be set by an environment variable, that is listed
         too. Values provided here take precedence over environment variables.
 
-        :param host: Host IP used to serve the application
+        :param host: Host IP used to serve the application, default to "127.0.0.1"
             env: ``HOST``
         :type host: string
 
-        :param port: Port used to serve the application
+        :param port: Port used to serve the application, default to "8050"
             env: ``PORT``
         :type port: int
 
@@ -2137,8 +2138,14 @@ def run(
 
         # Evaluate the env variables at runtime
 
-        host = host or os.getenv("HOST")
-        port = port or os.getenv("PORT")
+        if "CONDA_PREFIX" in os.environ:
+            # Some conda systems has issue with setting the host environment
+            # to an invalid hostname.
+            # Related issue: https://github.com/plotly/dash/issues/3069
+            host = host or "127.0.0.1"
+        else:
+            host = host or os.getenv("HOST", "127.0.0.1")
+        port = port or os.getenv("PORT", "8050")
         proxy = proxy or os.getenv("DASH_PROXY")
 
         # Verify port value