Fix python wrapper for layer_norm

paddle/operators/layer_norm_op.cc

@@ -116,8 +116,6 @@ class LayerNormGradOp : public framework::OperatorWithKernel {
     // check input
     PADDLE_ENFORCE(ctx->HasInput("X"),
                    "Input(X) of LayerNormOp should not be null.");
-    PADDLE_ENFORCE(ctx->HasInput("Scale"),
-                   "Input(Scale) of LayerNormOp should not be null.");
     PADDLE_ENFORCE(ctx->HasInput("Mean"),
                    "Input(Mean) of LayerNormOp should not be null.");
     PADDLE_ENFORCE(ctx->HasInput("Variance"),

python/paddle/v2/fluid/layers/nn.py

@@ -1637,7 +1637,7 @@ def layer_norm(input,
             dtype=dtype,
             default_initializer=Constant(1.0))
         inputs['Scale'] = scale
-    if center:
+    if shift:
         assert bias_attr is not False
         bias = helper.create_parameter(
             attr=helper.bias_attr, shape=param_shape, dtype=dtype, is_bias=True)