enhance input type chec for concat (#20584)

test=develop

python/paddle/fluid/layers/tensor.py

@@ -249,10 +249,15 @@ def concat(input, axis=0, name=None):
                 #  [14 15 16]]
     """
     helper = LayerHelper('concat', **locals())
+    if not isinstance(input, list):
+        warnings.warn(
+            "The type of input in concat should be list, but received %s." %
+            (type(input)))
+        input = [input]
     for x in input:
         if not isinstance(x, Variable):
             raise TypeError(
-                "The type of x in 'input' in concat must be Variable, but received %s"
+                "The type of x in 'input' in concat must be Variable, but received %s."
                 % (type(x)))
         if convert_dtype(x.dtype) in ['float16']:
             warnings.warn(

python/paddle/fluid/tests/unittests/test_concat_op.py

@@ -118,13 +118,22 @@ create_test_fp16(TestConcatOp5)
 class TestConcatOpError(OpTest):
     def test_errors(self):
         with program_guard(Program(), Program()):
-            # The input type of concat_op must be Variable.
-            x1 = fluid.create_lod_tensor(
+            # The input type of concat_op should be list.
+            x1 = fluid.layers.data(shape=[4], dtype='int32', name='x1')
+            fluid.layers.concat(x1)
+            # The item in input must be Variable.
+            x2 = fluid.create_lod_tensor(
                 np.array([[-1]]), [[1]], fluid.CPUPlace())
-            self.assertRaises(TypeError, fluid.layers.concat, x1)
+            x3 = fluid.create_lod_tensor(
+                np.array([[-1]]), [[1]], fluid.CPUPlace())
+            self.assertRaises(TypeError, fluid.layers.concat, [x2])
             # The input dtype of concat_op must be float16(only support on GPU), float32, float64, int32, int64.
-            x2 = fluid.layers.data(name='x2', shape=[4], dtype='uint8')
-            self.assertRaises(TypeError, fluid.layers.concat, x2)
+            x4 = fluid.layers.data(shape=[4], dtype='uint8', name='x4')
+            x5 = fluid.layers.data(shape=[4], dtype='uint8', name='x5')
+            self.assertRaises(TypeError, fluid.layers.concat, [x4, x5])
+            x6 = fluid.layers.data(shape=[4], dtype='float16', name='x6')
+            x7 = fluid.layers.data(shape=[4], dtype='float16', name='x7')
+            fluid.layers.concat([x6, x7])
 
 
 if __name__ == '__main__':