sage -n retrolab: New

src/bin/sage-notebook

@@ -93,9 +93,32 @@ class NotebookNbclassic(object):
             print("which includes support for interacts and the ability to download and")
             print("install other Jupyterlab extensions. For a minimal installation, run")
             print("  sage -i jupyterlab")
-            print("Alternatively, you can follow the instructions at")
-            print("  " + _system_jupyter_url)
-            print("to use Sage with an existing Jupyterlab installation.")
+            raise SystemExit(1)
+        self.print_banner()
+        main(argv)
+
+
+class NotebookRetrolab(object):
+    def print_banner(self):
+        banner()
+        print('Please wait while the Jupyterlab server starts...')
+
+    @classmethod
+    def print_help(cls):
+        cls(['help'])
+
+    def __init__(self, argv):
+        try:
+            from retrolab.app import main
+        except ImportError:
+            import traceback
+            traceback.print_exc()
+            print("Retrolab is not installed (at least not in this Sage installation).")
+            print("You can install it by running")
+            print("  sage -i jupyterlab_widgets retrolab")
+            print("which includes support for interacts and the ability to download and")
+            print("install other Jupyterlab extensions. For a minimal installation, run")
+            print("  sage -i retrolab")
             raise SystemExit(1)
         self.print_banner()
         main(argv)
@@ -168,9 +191,11 @@ notebook_launcher = {
     'jupyter': NotebookJupyter,
     'jupyterlab': NotebookJupyterlab,
     'nbclassic': NotebookNbclassic,
+    'retrolab': NotebookRetrolab,
     'export': SageNBExport,
 }
 
+
 notebook_names = ', '.join(notebook_launcher.keys())