diff --git a/python/jittor/nn.py b/python/jittor/nn.py
index 72620dc2..94019b1d 100644
--- a/python/jittor/nn.py
+++ b/python/jittor/nn.py
@@ -142,9 +142,10 @@ def get_init_var_rand(shape, dtype):
 def relu(x): return jt.maximum(x, 0)
 def leaky_relu(x, scale=0.01): return jt.ternary(x>0, x, x*scale)
 def relu6(x): return jt.minimum(jt.maximum(x, 0), 6)
-def sign(x): 
-    x = jt.ternary(x>0, jt.ones(x.shape), x)
-    return jt.ternary(x<0, -1*jt.ones(x.shape), x)
+def sign(x):
+    one = jt.ones(x.shape)
+    x = jt.ternary(x>0, one, x)
+    return jt.ternary(x<0, -one, x)
 
 def gelu(x):
     _sqrt2 = 1.4142135623730951
@@ -1173,9 +1174,6 @@ class Sequential(Module):
                     self.append(m)
             else:
                 self.append(mod)
-    def __iter__(self):
-        for v in self.layers.values():
-            yield v
     def __getitem__(self, idx):
         return self.layers[idx]
     def __iter__(self):