strip static url trailing slash at assignment

flask/app.py

@@ -408,11 +408,8 @@ class Flask(_PackageBoundObject):
             self, import_name, template_folder=template_folder, root_path=root_path
         )
 
-        if static_url_path is not None:
-            self.static_url_path = static_url_path
-
-        if static_folder is not None:
-            self.static_folder = static_folder
+        self.static_url_path = static_url_path
+        self.static_folder = static_folder
 
         if instance_path is None:
             instance_path = self.auto_find_instance_path()
@@ -594,7 +591,7 @@ class Flask(_PackageBoundObject):
                 bool(static_host) == host_matching
             ), "Invalid static_host/host_matching combination"
             self.add_url_rule(
-                self.static_url_path.rstrip("/") + "/<path:filename>",
+                self.static_url_path + "/<path:filename>",
                 endpoint="static",
                 host=static_host,
                 view_func=self.send_static_file,

flask/blueprints.py

@@ -208,7 +208,7 @@ class Blueprint(_PackageBoundObject):
 
         if self.has_static_folder:
             state.add_url_rule(
-                self.static_url_path.rstrip("/") + "/<path:filename>",
+                self.static_url_path + "/<path:filename>",
                 view_func=self.send_static_file,
                 endpoint="static",
             )

flask/helpers.py

@@ -965,24 +965,27 @@ class _PackageBoundObject(object):
     )
     del _get_static_folder, _set_static_folder
 
-    def _get_static_url_path(self):
+    @property
+    def static_url_path(self):
+        """The URL prefix that the static route will be accessible from.
+
+        If it was not configured during init, it is derived from
+        :attr:`static_folder`.
+        """
         if self._static_url_path is not None:
             return self._static_url_path
 
         if self.static_folder is not None:
             basename = os.path.basename(self.static_folder)
-            return "/" + basename if basename else ""
+            return ("/" + basename).rstrip("/")
+
+    @static_url_path.setter
+    def static_url_path(self, value):
+        if value is not None:
+            value = value.rstrip("/")
 
-    def _set_static_url_path(self, value):
         self._static_url_path = value
 
-    static_url_path = property(
-        _get_static_url_path,
-        _set_static_url_path,
-        doc="The URL prefix that the static route will be registered for.",
-    )
-    del _get_static_url_path, _set_static_url_path
-
     @property
     def has_static_folder(self):
         """This is ``True`` if the package bound object's container has a