Keras AttributeError: ‘list’ object has no attribute ‘ndim’

I’m running a Keras neural network model in Jupyter Notebook (Python 3.6)

I get the following error

AttributeError: ‘list’ object has no attribute ‘ndim’

after calling the .fit() method from Keras.model

model  = Sequential()
model.add(Dense(5, input_dim=len(X_data[0]), activation='sigmoid' ))
model.add(Dense(1, activation = 'sigmoid'))
model.compile(loss='mean_squared_error', optimizer='adam', metrics=['acc'])
model.fit(X_data, y_data, epochs=20, batch_size=10)

I checked the requirements.txt file for Keras (in Anaconda3) and the numpy, scipy, and six module versions are all up to date.

What can explain this AttributeError?

The full error message is the following (seems to be somewhat related to Numpy):

————————————————————————— AttributeError Traceback (most recent call
last) in ()
3 model.add(Dense(1, activation = ‘sigmoid’))
4 model.compile(loss=’mean_squared_error’, optimizer=’adam’, metrics=[‘acc’])
—-> 5 model.fit(X_data, y_data, epochs=20, batch_size=10)

~\Anaconda3\lib\site-packages\keras\models.py in fit(self, x, y,
batch_size, epochs, verbose, callbacks, validation_split,
validation_data, shuffle, class_weight, sample_weight, initial_epoch,
steps_per_epoch, validation_steps, **kwargs)
963 initial_epoch=initial_epoch,
964 steps_per_epoch=steps_per_epoch,
–> 965 validation_steps=validation_steps)
966
967 def evaluate(self, x=None, y=None,

~\Anaconda3\lib\site-packages\keras\engine\training.py in fit(self, x,
y, batch_size, epochs, verbose, callbacks, validation_split,
validation_data, shuffle, class_weight, sample_weight, initial_epoch,
steps_per_epoch, validation_steps, **kwargs) 1591
class_weight=class_weight, 1592 check_batch_axis=False,
-> 1593 batch_size=batch_size) 1594 # Prepare validation data. 1595 do_validation = False

~\Anaconda3\lib\site-packages\keras\engine\training.py in
_standardize_user_data(self, x, y, sample_weight, class_weight, check_batch_axis, batch_size) 1424
self._feed_input_shapes, 1425
check_batch_axis=False,
-> 1426 exception_prefix=’input’) 1427 y = _standardize_input_data(y, self._feed_output_names,
1428 output_shapes,

~\Anaconda3\lib\site-packages\keras\engine\training.py in
_standardize_input_data(data, names, shapes, check_batch_axis, exception_prefix)
68 elif isinstance(data, list):
69 data = [x.values if x.class.name == ‘DataFrame’ else x for x in data]
—> 70 data = [np.expand_dims(x, 1) if x is not None and x.ndim == 1 else x for x in data]
71 else:
72 data = data.values if data.class.name == ‘DataFrame’ else data

~\Anaconda3\lib\site-packages\keras\engine\training.py in
(.0)
68 elif isinstance(data, list):
69 data = [x.values if x.class.name == ‘DataFrame’ else x for x in data]
—> 70 data = [np.expand_dims(x, 1) if x is not None and x.ndim == 1 else x for x in data]
71 else:
72 data = data.values if data.class.name == ‘DataFrame’ else data

AttributeError: ‘list’ object has no attribute ‘ndim’