From c8e8fd0378b3bce66e27144f9bc7c5de517ef2c8 2021-03-14 00:49:28
From: Blazej Michalik <blazej.michalik@nokia.com>
Date: 2021-03-14 00:49:28
Subject: [PATCH] Fix IndexError on a singular slash input

---

diff --git a/IPython/core/inputtransformer2.py b/IPython/core/inputtransformer2.py
index a5229ae..c7deab8 100644
--- a/IPython/core/inputtransformer2.py
+++ b/IPython/core/inputtransformer2.py
@@ -678,7 +678,11 @@ class TransformerManager:
 
         # Bail if we got one line and there are more closing parentheses than
         # the opening ones
-        if len(lines) == 1 and has_sunken_brackets(tokens_by_line[0]):
+        if (
+            len(lines) == 1
+            and tokens_by_line
+            and has_sunken_brackets(tokens_by_line[0])
+        ):
             return "invalid", None
 
         if not tokens_by_line: