diff --git a/python/tvm/relay/frontend/onnx.py b/python/tvm/relay/frontend/onnx.py
index a5ae959901ba..3321462573ad 100644
--- a/python/tvm/relay/frontend/onnx.py
+++ b/python/tvm/relay/frontend/onnx.py
@@ -64,54 +64,16 @@
 }
 
 
-class onnx_input:
-    """Dual purpose list or dictionary access object."""
-
-    def __init__(self):
-        self.input_keys = []
-        self.input_dict = {}
+class onnx_input(list):
+    """A helper extension to list that returns None for out of bound indices."""
 
     def __getitem__(self, item):
-        if isinstance(item, int):
-            if item > (len(self.input_keys) - 1):
-                return None
-            return self.input_dict[self.input_keys[item]]
-        if isinstance(item, str):
-            if item not in self.input_keys:
-                return None
-            return self.input_dict[item]
         if isinstance(item, slice):
-            keys = self.input_keys[item]
-            return [self.input_dict[key] for key in keys]
-
-        raise ValueError("Only integer, string, and slice accesses allowed.")
-
-    def __setitem__(self, item, value):
+            indices = list(range(item.stop)[item])
+            return [self[i] for i in indices]
         if isinstance(item, int):
-            self.input_dict[self.input_keys[item]] = value
-        elif isinstance(item, str):
-            self.input_keys.append(item)
-            self.input_dict[item] = value
-        else:
-            raise ValueError("Only integer and string indexed writes allowed.")
-
-    def keys(self):
-        return self.input_keys
-
-    def __len__(self):
-        return len(self.input_keys)
-
-    def __iter__(self):
-        self.n = 0
-        return self
-
-    def __next__(self):
-        if self.n < len(self.input_keys):
-            output = self.input_dict[self.input_keys[self.n]]
-            self.n += 1
-            return output
-
-        raise StopIteration
+            return list(self)[item] if item < len(self) else None
+        raise TypeError("list indices must be integers or slices, not %s" % type(item).__name__)
 
 
 def get_numpy(tensor_proto):
@@ -2673,6 +2635,19 @@ def _impl_v10(cls, inputs, attr, params):
         return isinf
 
 
+class Celu(OnnxOpConverter):
+    """Operator convereter for celu"""
+
+    @classmethod
+    def _impl_v12(cls, inputs, attr, params):
+        x = inputs[0]
+        dtype = infer_type(x).checked_type.dtype
+        alpha = _op.const(attr.get("alpha", 1.0), dtype)
+        zero = _op.const(0, dtype)
+        one = _op.const(1, dtype)
+        return _op.maximum(zero, x) + _op.minimum(zero, alpha * (_op.exp(x / alpha) - one))
+
+
 class MaxRoiPool(OnnxOpConverter):
     """Operator converter for MaxRoiPool."""
 
@@ -3881,13 +3856,13 @@ def from_onnx(self, graph, opset, get_output_expr=False):
         for node in graph.node:
             op_name = node.op_type
             attr = self._parse_attr(node.attribute)
-            # Create and populate onnx input object.
+            # Create and populate input list.
             inputs = onnx_input()
             for i in node.input:
                 if i != "":
-                    inputs[i] = self._nodes[self._renames.get(i, i)]
+                    inputs.append(self._nodes[self._renames.get(i, i)])
                 else:
-                    inputs[i] = None
+                    inputs.append(None)
             i_name = self._parse_value_proto(node)
             node_output = self._fix_outputs(op_name, node.output)
             attr["tvm_custom"] = {}
@@ -4040,19 +4015,6 @@ def _fix_outputs(self, op_name, outputs):
         return outputs
 
 
-class Celu(OnnxOpConverter):
-    """Operator convereter for celu"""
-
-    @classmethod
-    def _impl_v12(cls, inputs, attr, params):
-        x = inputs[0]
-        dtype = infer_type(x).checked_type.dtype
-        alpha = _op.const(attr.get("alpha", 1.0), dtype)
-        zero = _op.const(0, dtype)
-        one = _op.const(1, dtype)
-        return _op.maximum(zero, x) + _op.minimum(zero, alpha * (_op.exp(x / alpha) - one))
-
-
 def from_onnx(
     model, shape=None, dtype="float32", opset=None, freeze_params=False, convert_config=None
 ):