Output of fixed size iterator needes element constructor

src/sage/combinat/plane_partition.py

@@ -1123,7 +1123,7 @@ def P_in_shape_iter(n, la):
         for m in range(n,0,-1):
             for la in Partitions(m):
                 for a in PP_first_row_iter(n,la):
-                    yield a
+                    yield PlanePartition(a)