Change assertion in topological sorting

1 files changed, 6 insertions, 3 deletions

diff --git a/src/pip/_internal/resolution/resolvelib/resolver.py b/src/pip/_internal/resolution/resolvelib/resolver.py
index cb7d1ae8a..718619b51 100644
--- a/src/pip/_internal/resolution/resolvelib/resolver.py
+++ b/src/pip/_internal/resolution/resolvelib/resolver.py
@@ -180,7 +180,10 @@ class Resolver(BaseResolver):
         assert self._result is not None, "must call resolve() first"
 
         graph = self._result.graph
-        weights = get_topological_weights(graph)
+        weights = get_topological_weights(
+            graph,
+            expected_node_count=len(self._result.mapping) + 1,
+        )
 
         sorted_items = sorted(
             req_set.requirements.items(),
@@ -190,7 +193,7 @@ class Resolver(BaseResolver):
         return [ireq for _, ireq in sorted_items]
 
 
-def get_topological_weights(graph):
+def get_topological_weights(graph, expected_node_count):
     # type: (Graph) -> Dict[Optional[str], int]
     """Assign weights to each node based on how "deep" they are.
 
@@ -231,7 +234,7 @@ def get_topological_weights(graph):
 
     # Sanity checks
     assert weights[None] == 0
-    assert len(weights) == len(graph)
+    assert len(weights) == expected_node_count
 
     return weights