python2 compatibility

Author: LBrunswic

src/sage/tensor/modules/tensor_with_indices.py

@@ -931,14 +931,15 @@ def permute_indices(self, permutation):
         swap_params = list(combinations(range(self._tensor.tensor_rank()+1), 3))
 
         # The associated permutation is as follows
-        def swap(i,j,k,N):
+        def swap(param,N):
+            i,j,k = param
             L = list(range(1,N+1))
             L = L[:i] + L[j:k] + L[i:j] + L[k:]
             return L
 
         # Construction of the permutation group generated by swaps
         perm_group = PermutationGroup(
-            [swap(*param, self._tensor.tensor_rank()) for param in swap_params],
+            [swap(param, self._tensor.tensor_rank()) for param in swap_params],
             canonicalize = False
         )
         # Compute a decomposition of the permutation as a product of swaps