diff --git a/paddle/framework/operator.cc b/paddle/framework/operator.cc
index 4d327958843e00fe43657abe074bbbbd1364afbc..68fb469b561618ec838045a76d903bcfb805c06f 100644
--- a/paddle/framework/operator.cc
+++ b/paddle/framework/operator.cc
@@ -35,16 +35,10 @@ ExecutionContext::GetEigenDevice<platform::GPUPlace, Eigen::GpuDevice>() const {
 
 std::string OperatorBase::Input(const std::string& name) const {
   auto& ins = Inputs(name);
-  switch (ins.size()) {
-    case 0:
-      return kEmptyVarName;
-    case 1:
-      return ins[0];
-    default:
-      PADDLE_THROW("Op %s input %s should contain only one variable", type_,
-                   name);
-      return "";
-  }
+  PADDLE_ENFORCE_LE(ins.size(), 1UL,
+                    "Op %s input %s should contain only one variable", type_,
+                    name);
+  return ins.empty() ? kEmptyVarName : ins[0];
 }
 
 const std::vector<std::string>& OperatorBase::Inputs(
@@ -57,16 +51,10 @@ const std::vector<std::string>& OperatorBase::Inputs(
 
 std::string OperatorBase::Output(const std::string& name) const {
   auto& outs = Outputs(name);
-  switch (outs.size()) {
-    case 0:
-      return kEmptyVarName;
-    case 1:
-      return outs[0];
-    default:
-      PADDLE_THROW("Op %s output %s should contain only one variable", type_,
-                   name);
-      return "";
-  }
+  PADDLE_ENFORCE_LE(outs.size(), 1UL,
+                    "Op %s output %s should contain only one variable", type_,
+                    name);
+  return outs.empty() ? kEmptyVarName : outs[0];
 }
 
 const std::vector<std::string>& OperatorBase::Outputs(
diff --git a/paddle/framework/operator.h b/paddle/framework/operator.h
index 7759473ef303dbc73abc79dd5b053828742f4951..60ca8b279e75f7ade7183ea8b818708ced6dd05f 100644
--- a/paddle/framework/operator.h
+++ b/paddle/framework/operator.h
@@ -239,20 +239,12 @@ class InferShapeContext {
 
   const Variable* InputVar(const std::string& name) const {
     auto ipt = op_.Input(name);
-    if (ipt == kEmptyVarName) {
-      return nullptr;
-    } else {
-      return scope_.FindVar(ipt);
-    }
+    return ipt == kEmptyVarName ? nullptr : scope_.FindVar(ipt);
   }
 
   Variable* OutputVar(const std::string& name) const {
     auto opt = op_.Output(name);
-    if (opt == kEmptyVarName) {
-      return nullptr;
-    } else {
-      return scope_.FindVar(opt);
-    }
+    return opt == kEmptyVarName ? nullptr : scope_.FindVar(opt);
   }
 
   const std::vector<const Variable*> MultiInputVar(
@@ -262,8 +254,8 @@ class InferShapeContext {
     res.reserve(names.size());
     std::transform(names.begin(), names.end(), std::back_inserter(res),
                    [this](const std::string& name) {
-                     return name != kEmptyVarName ? scope_.FindVar(name)
-                                                  : nullptr;
+                     return name == kEmptyVarName ? nullptr
+                                                  : scope_.FindVar(name);
                    });
     return res;
   }
@@ -274,8 +266,8 @@ class InferShapeContext {
     res.reserve(names.size());
     std::transform(names.begin(), names.end(), std::back_inserter(res),
                    [this](const std::string& name) {
-                     return name != kEmptyVarName ? scope_.FindVar(name)
-                                                  : nullptr;
+                     return name == kEmptyVarName ? nullptr
+                                                  : scope_.FindVar(name);
                    });
     return res;
   }