TypeError: object of type 'NoneType' has no len() when implementing neural network

Question

I am building artificial neuron network (ANN) model for predicting values but facing problem:

Input:

def create_model(optimizer = 'rmsprop', units = 16, learning_rate = 0.001):

ann = tf.keras.Sequential() # Initialising ANN
ann.add(tf.keras.layers.Dense(units = units, activation = "relu")) # Adding First Hidden Layer
ann.add(tf.keras.layers.Dense(units = units, activation = "relu")) # Adding Second Hidden Layer
ann.add(tf.keras.layers.Dense(units = Y.shape[1], activation = 'softmax')) # Adding Output Layer

###############################################
# Add optimizer with learning rate
if optimizer == 'rmsprop':
    opt = tf.keras.optimizers.RMSprop(learning_rate = learning_rate)
elif optimizer == 'adam':
    opt = tf.keras.optimizers.Adam(learning_rate = learning_rate)
elif optimizer == 'SGD':
    opt = tf.keras.optimizers.SGD(learning_rate = learning_rate)
else:
    raise ValueError('optimizer {} unrecognized'.format(optimizer))
############################################## 

ann.compile(optimizer = optimizer, loss = 'categorical_crossentropy',  metrics = ['accuracy']) # Compiling ANN
return ann

ann = KerasClassifier(model = create_model, 
                     verbose = 2, 
                     learning_rate = 0.001, 
                     units = 16
                     )

optimizers = ['rmsprop', 'adam', 'SGD']
epoch_values = [10, 25, 50, 100, 150, 200]
batches = [10, 20, 30, 40, 50, 100, 1000]
units = [16, 32, 64, 128, 256]
lr_values = [0.001, 0.01, 0.1, 0.2, 0.3]

hyperparameters = dict(optimizer = optimizers, 
                        epochs = epoch_values, 
                        batch_size = batches, 
                        units = units,
                        learning_rate = lr_values
                        )

grid = GridSearchCV(estimator = ann, cv = 5, param_grid = hyperparameters)

history = grid.fit(X_train, 
                 Y_train, 
                 batch_size = 32, 
                 validation_data = (X_test, Y_test), 
                 epochs = 100
                 ) # Fitting ANN

Output error:

    File c:\Users\dis\AppData\Local\Programs\Python\Python310\lib\site-packages\sklearn\model_selection\_search.py:875, in BaseSearchCV.fit(self, X, y, groups, **fit_params)
    869     results = self._format_results(
    870         all_candidate_params, n_splits, all_out, all_more_results
    871     )
    873     return results
--> 875 self._run_search(evaluate_candidates)
    877 # multimetric is determined here because in the case of a callable
    878 # self.scoring the return type is only known after calling
...
    self._check_model_compatibility(y)
  File "c:\Users\dis\AppData\Local\Programs\Python\Python310\lib\site-packages\scikeras\wrappers.py", line 551, in _check_model_compatibility
    if self.n_outputs_expected_ != len(self.model_.outputs):
TypeError: object of type 'NoneType' has no len()

Data:

• X.shape -> (10, 2066)
• Y.shape -> (10, 4)
• X_train.shape -> (8, 2066)
• X_test.shape -> (2, 2066)
• Y_train.shape -> (8, 4)
• Y_test.shape -> (2, 4)

Answer 1

When you use Sequential model in tf.keras you need to provide the input_shape in the first layer or to add the input layer.

Modify your code as follows:

ann = tf.keras.Sequential() # Initialising ANN
ann.add(tf.keras.layers.Dense(units = units, input_shape=(X.shape[0],), activation = "relu")) # Adding First Hidden Layer
ann.add(tf.keras.layers.Dense(units = units, activation = "relu")) # Adding Second Hidden Layer
ann.add(tf.keras.layers.Dense(units = Y.shape[1], activation = 'softmax')) # Adding Output Layer

or adding an input layer as follows:

ann = tf.keras.Sequential() # Initialising ANN
ann.add(tf.keras.layers.Input(shape=(X.shape[0],))) # Input Layer
ann.add(tf.keras.layers.Dense(units = units, activation = "relu")) # Adding First Hidden Layer
ann.add(tf.keras.layers.Dense(units = units, activation = "relu")) # Adding Second Hidden Layer
ann.add(tf.keras.layers.Dense(units = Y.shape[1], activation = 'softmax')) # Adding Output Layer