tf.train.import_meta_graph passed.

src/TensorFlowNET.Core/Framework/meta_graph.py.cs

@@ -18,7 +18,7 @@ namespace Tensorflow
             return meta_graph_def;
         }
 
-        public static (RefVariable[], string[]) import_scoped_meta_graph_with_return_elements(MetaGraphDef meta_graph_or_file,
+        public static (Dictionary<string, RefVariable>, ITensorOrOperation[]) import_scoped_meta_graph_with_return_elements(MetaGraphDef meta_graph_or_file,
             bool clear_devices = false,
             string import_scope = "",
             Dictionary<string, Tensor> input_map = null,
@@ -89,7 +89,7 @@ namespace Tensorflow
                                     variable = new RefVariable(variable_def: proto, import_scope: scope_to_prepend_to_names);
                                     variable_objects[value] = variable;
                                 }
-                                
+                                variable = variable_objects[value];
                                 graph.add_to_collection(col.Key, variable);
                             }
                         }
@@ -102,7 +102,12 @@ namespace Tensorflow
                 }
             }
 
-            return (null, null);
+            var variables = graph.get_collection(ops.GraphKeys.GLOBAL_VARIABLES,
+                                     scope: scope_to_prepend_to_names) as List<RefVariable>;
+            var var_list = new Dictionary<string, RefVariable>();
+            variables.ForEach(v => var_list[ops.strip_name_scope(v.name, scope_to_prepend_to_names)] = v);
+
+            return (var_list, imported_return_elements);
         }
 
         /// <summary>

src/TensorFlowNET.Core/Graphs/Graph.cs

@@ -26,6 +26,12 @@ namespace Tensorflow
         public string _graph_key;
         public Status Status { get; }
 
+        /// <summary>
+        /// True if the graph is considered "finalized".  In that case no
+        /// new operations can be added.
+        /// </summary>
+        private bool _finalized = false;
+
         /// <summary>
         /// Arbitrary collections of objects.
         /// </summary>
@@ -126,6 +132,7 @@ namespace Tensorflow
 
         public void add_to_collection<T>(string name, T value)
         {
+            _check_not_finalized();
             if (_collections.ContainsKey(name))
                 (_collections[name] as List<T>).Add(value);
             else
@@ -138,6 +145,12 @@ namespace Tensorflow
                 add_to_collection(name, value);
         }
 
+        private void _check_not_finalized()
+        {
+            if (_finalized)
+                throw new RuntimeError("Graph is finalized and cannot be modified.");
+        }
+
         public unsafe Operation create_op(string op_type, Tensor[] inputs, TF_DataType[] dtypes, 
             TF_DataType[] input_types = null, string name = "", 
             Dictionary<string, AttrValue> attrs = null, OpDef op_def = null)

src/TensorFlowNET.Core/Train/Saving/BaseSaverBuilder.cs

@@ -85,8 +85,8 @@ namespace Tensorflow
 
                 // Add a placeholder string tensor for the filename.
                 var filename_tensor = array_ops.placeholder_with_default(string.IsNullOrEmpty(filename) ? "model" : filename, shape: new int[0], name: "filename");
-                filename_tensor = gen_array_ops.placeholder_with_default(filename_tensor, shape: new int[0], name: "Const");
                 // Keep the name "Const" for backwards compatibility.
+                filename_tensor = gen_array_ops.placeholder_with_default(filename_tensor, shape: new int[0], name: "Const");
 
                 // Add the save ops.
                 if (sharded)
@@ -106,10 +106,19 @@ namespace Tensorflow
                 var check_collection_list = graph.get_all_collection_keys();
                 foreach (var collection_type in check_collection_list)
                 {
-                    foreach (var element in graph.get_collection(collection_type) as IList<RefVariable>)
+                    var cols = graph.get_collection(collection_type);
+                    switch (cols)
                     {
-
+                        case List<RefVariable> values:
+                            foreach (var element in values) ;
+                            break;
+                        case List<ITensorOrOperation> values:
+                            foreach (var element in values) ;
+                            break;
+                        default:
+                            throw new NotImplementedException("_build_internal.check_collection_list");
                     }
+                    
                 }
 
                 return new SaverDef()

src/TensorFlowNET.Core/Train/Saving/Saver.cs

@@ -193,7 +193,7 @@ namespace Tensorflow
             return _is_empty ? string.Empty : model_checkpoint_path;
         }
 
-        public Saver import_meta_graph(string meta_graph_or_file, 
+        public (Saver, object) import_meta_graph(string meta_graph_or_file, 
             bool clear_devices = false,
             string import_scope = "")
         {

src/TensorFlowNET.Core/Train/Saving/saver.py.cs

@@ -6,22 +6,48 @@ namespace Tensorflow
 {
     public class saver
     {
-        public static Saver _import_meta_graph_with_return_elements(string meta_graph_or_file,
+        public static (Saver, object) _import_meta_graph_with_return_elements(string meta_graph_or_file,
             bool clear_devices = false,
             string import_scope = "",
             string[] return_elements = null)
         {
             var meta_graph_def = meta_graph.read_meta_graph_file(meta_graph_or_file);
 
-            meta_graph.import_scoped_meta_graph_with_return_elements(
+            var imported_vars = meta_graph.import_scoped_meta_graph_with_return_elements(
                         meta_graph_def,
                         clear_devices: clear_devices,
                         import_scope: import_scope,
                         return_elements: return_elements);
 
-            return null;
-            /*var (imported_vars, imported_return_elements) = (
-                    , false);*/
+            var saver = _create_saver_from_imported_meta_graph(
+                meta_graph_def, import_scope, imported_vars);
+
+            return (saver, null);
+        }
+
+        public static Saver _create_saver_from_imported_meta_graph(MetaGraphDef meta_graph_def, 
+            string import_scope, 
+            (Dictionary<string, RefVariable>, ITensorOrOperation[]) imported_vars)
+        {
+            if(meta_graph_def.SaverDef != null)
+            {
+                throw new NotImplementedException("_create_saver_from_imported_meta_graph");
+            }
+            else
+            {
+                if(variables._all_saveable_objects(scope: import_scope).Length > 0)
+                {
+                    // Return the default saver instance for all graph variables.
+                    return new Saver();
+                }
+                else
+                {
+                    // If no graph variables exist, then a Saver cannot be constructed.
+                    Console.WriteLine("Saver not created because there are no variables in the" +
+                        " graph to restore");
+                    return null;
+                }
+            }
         }
     }
 }

src/TensorFlowNET.Core/Train/tf.optimizers.cs

@@ -19,7 +19,7 @@ namespace Tensorflow
                 bool clear_devices = false,
                 string import_scope = "") => saver._import_meta_graph_with_return_elements(meta_graph_or_file,
                     clear_devices,
-                    import_scope);
+                    import_scope).Item1;
         }
     }
 }

src/TensorFlowNET.Core/ops.GraphKeys.cs

@@ -28,7 +28,7 @@ namespace Tensorflow
             /// </summary>
             public static string GLOBAL_VARIABLES = "variables";
 
-            public static string[] _VARIABLE_COLLECTIONS = new string[] { "trainable_variables" }; 
+            public static string[] _VARIABLE_COLLECTIONS = new string[] { "variables", "trainable_variables" }; 
             /// <summary>
             /// Key to collect BaseSaverBuilder.SaveableObject instances for checkpointing.
             /// </summary>

src/TensorFlowNET.Core/ops.py.cs

@@ -440,5 +440,17 @@ namespace Tensorflow
                     throw new NotImplementedException($"internal_convert_to_tensor: Can't convert {value.GetType().Name} to Tensor");
             }
         }
+
+        public static string strip_name_scope(string name, string export_scope = "")
+        {
+            if (!string.IsNullOrEmpty(export_scope))
+            {
+                throw new NotImplementedException("ops.strip_name_scope");
+            }
+            else
+            {
+                return name;
+            }
+        }
     }
 }