diff --git a/msccl/language/instruction_dag.py b/msccl/language/instruction_dag.py
index 5c859d5..60f1867 100755
--- a/msccl/language/instruction_dag.py
+++ b/msccl/language/instruction_dag.py
@@ -145,10 +145,10 @@ def _read(self, rank, buffer, index, size, op):
 
     def _infer_dependencies(self):
         visited = set()
-        for slot, ops in self.operations.items():
-            if ops in visited:
+        for _, op in self.operations.items():
+            if op in visited:
                 continue
-            frontier = [ops]
+            frontier = [op]
             while len(frontier) > 0:
                 op = frontier[0]
                 if op in visited:
@@ -315,6 +315,7 @@ def optimize(self):
     # Completes metadata for chunk_steps (number of steps from a start op) and priority (number of steps to the last op)
     def _complete_metadata(self):
         visited = set()
+
         def dfs(op, cs):
             # already visited and no need to update chunk_step
             if op.chunk_step >= cs + 1 and op in visited:
@@ -348,10 +349,10 @@ def dfs(op, cs):
     # recv(src, sbuf, si, _, _, _ ) send(_, _, _, dst, dbuf, di) -> recv_copy_send(src, sbuf, si, dst, dbuf, di)
     def _optimize_rcs(self):
         visited = set()
-        for slot, ops in self.operations.items():
-            if ops in visited:
+        for _, op in self.operations.items():
+            if op in visited:
                 continue
-            frontier = [ops]
+            frontier = [op]
             while len(frontier) > 0:
                 op = frontier[0]
                 if op in visited:
@@ -382,10 +383,10 @@ def _optimize_rcs(self):
     def _optimize_rrcs_rrs(self):
         # RRC/S -> RRS
         visited = set()
-        for slot, ops in self.operations.items():
-            if ops in visited:
+        for _, op in self.operations.items():
+            if op in visited:
                 continue
-            frontier = [ops]
+            frontier = [op]
             while len(frontier) > 0:
                 op = frontier[0]
                 if op in visited: