Improved error for removed attributes

Author: T4rk1n

dash/_obsolete.py

@@ -0,0 +1,23 @@
+# pylint: disable=too-few-public-methods
+from .exceptions import ObsoleteAttributeException
+
+
+class ObsoleteAttribute:
+    def __init__(self, message: str, exc=ObsoleteAttributeException):
+        self.message = message
+        self.exc = exc
+
+
+class ObsoleteChecker:
+    _obsolete_attributes = {
+        "run_server": ObsoleteAttribute("app.run_server has been replaced by app.run"),
+        "long_callback": ObsoleteAttribute(
+            "app.long_callback has been  removed, use app.callback(..., background=True) instead"
+        ),
+    }
+
+    def __getattr__(self, name: str):
+        if name in self._obsolete_attributes:
+            err = self._obsolete_attributes[name]
+            raise err.exc(err.message)
+        return getattr(self, name)

dash/dash.py

@@ -66,6 +66,7 @@
 from . import _get_app
 
 from ._grouping import map_grouping, grouping_len, update_args_group
+from ._obsolete import ObsoleteChecker
 
 from . import _pages
 from ._pages import (
@@ -194,7 +195,7 @@ def _do_skip(error):
 
 # pylint: disable=too-many-instance-attributes
 # pylint: disable=too-many-arguments, too-many-locals
-class Dash:
+class Dash(ObsoleteChecker):
     """Dash is a framework for building analytical web applications.
     No JavaScript required.
 

dash/exceptions.py

@@ -10,6 +10,10 @@ class ObsoleteKwargException(DashException):
     pass
 
 
+class ObsoleteAttributeException(DashException):
+    pass
+
+
 class NoLayoutException(DashException):
     pass