[@to_static]Enhance error msg in paddle.assign in static mode (#38069)

* Enhance error msg in paddle.assign in static mode

* fix unittest

python/paddle/fluid/layers/tensor.py

@@ -616,6 +616,11 @@ def assign(input, output=None):
         helper.append_op(
             type='assign', inputs={'X': [input]}, outputs={'Out': [output]})
     elif isinstance(input, numpy.ndarray):
+        # Not support [var, var, ...] currently.
+        if len(input.shape) > 0 and any(isinstance(x, Variable) for x in input):
+            raise TypeError(
+                "Required type(input) numpy.ndarray, but found `list(Variable)` in input."
+            )
         dtype = convert_np_dtype_to_dtype_(input.dtype)
         if dtype == VarDesc.VarType.FP64:
             # Setting FP64 numpy data is not supported in Paddle, so we

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

@@ -181,6 +181,13 @@ class TestAssignOpErrorApi(unittest.TestCase):
             x2 = np.array([[2.5, 2.5]], dtype='uint8')
             self.assertRaises(TypeError, paddle.assign, x2)
 
+    def test_type_error(self):
+        paddle.enable_static()
+        with program_guard(Program(), Program()):
+            x = [paddle.randn([3, 3]), paddle.randn([3, 3])]
+            # not support to assign list(var)
+            self.assertRaises(TypeError, paddle.assign, x)
+
 
 if __name__ == '__main__':
     paddle.enable_static()