From b31f288dc0a9663d5088ab065abf14d3a9c9f471 Mon Sep 17 00:00:00 2001
From: Rajat Mittal <rajat.mttl@gmail.com>
Date: Sun, 26 May 2019 16:31:02 +0800
Subject: [PATCH] added one line

---
 src/sage/graphs/base/c_graph.pyx | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/sage/graphs/base/c_graph.pyx b/src/sage/graphs/base/c_graph.pyx
index 89972d1f7cc..02c64ecf992 100644
--- a/src/sage/graphs/base/c_graph.pyx
+++ b/src/sage/graphs/base/c_graph.pyx
@@ -2195,7 +2195,8 @@ cdef class CGraphBackend(GenericGraphBackend):
             sage: G.distance(0, 5, by_weight=true)
             3
         """
-
+        if exclude_vertices and (x in exclude_vertices or y in exclude_vertices):
+            raise LookupError("No path between %s and %s" % (x, y))
         if x == y:
             return 0