The Sequential model API

To get started, read this guide to the Keras Sequential model.

Useful attributes of Model

  • model.layers is a list of the layers added to the model.

Sequential model methods

compile

compile(self, optimizer, loss, metrics=[], sample_weight_mode=None)

Configures the learning process.

Arguments

  • optimizer: str (name of optimizer) or optimizer object. See optimizers.
  • loss: str (name of objective function) or objective function. See objectives.
  • metrics: list of metrics to be evaluated by the model during training and testing. Typically you will use metrics=['accuracy'].
  • sample_weight_mode: if you need to do timestep-wise sample weighting (2D weights), set this to "temporal". "None" defaults to sample-wise weights (1D).
  • kwargs: for Theano backend, these are passed into K.function. Ignored for Tensorflow backend.

Example

    model = Sequential()
    model.add(Dense(32, input_shape=(500,)))
    model.add(Dense(10, activation='softmax'))
    model.compile(optimizer='rmsprop',
          loss='categorical_crossentropy',
          metrics=['acccuracy'])

fit

fit(self, x, y, batch_size=32, nb_epoch=10, verbose=1, callbacks=[], validation_split=0.0, validation_data=None, shuffle=True, class_weight=None, sample_weight=None)

Trains the model for a fixed number of epochs.

Arguments

  • x: input data, as a Numpy array or list of Numpy arrays (if the model has multiple inputs).
  • y: labels, as a Numpy array.
  • batch_size: integer. Number of samples per gradient update.
  • nb_epoch: integer, the number of epochs to train the model.
  • verbose: 0 for no logging to stdout, 1 for progress bar logging, 2 for one log line per epoch.
  • callbacks: list of keras.callbacks.Callback instances. List of callbacks to apply during training. See callbacks.
  • validation_split: float (0. < x < 1). Fraction of the data to use as held-out validation data.
  • validation_data: tuple (X, y) to be used as held-out validation data. Will override validation_split.
  • shuffle: boolean or str (for 'batch'). Whether to shuffle the samples at each epoch. 'batch' is a special option for dealing with the limitations of HDF5 data; it shuffles in batch-sized chunks.
  • class_weight: dictionary mapping classes to a weight value, used for scaling the loss function (during training only).
  • sample_weight: Numpy array of weights for the training samples, used for scaling the loss function (during training only). You can either pass a flat (1D) Numpy array with the same length as the input samples
    • (1:1 mapping between weights and samples), or in the case of temporal data, you can pass a 2D array with shape (samples, sequence_length), to apply a different weight to every timestep of every sample. In this case you should make sure to specify sample_weight_mode="temporal" in compile().

Returns

A History object. Its History.history attribute is a record of training loss values and metrics values at successive epochs, as well as validation loss values and validation metrics values (if applicable).

evaluate

evaluate(self, x, y, batch_size=32, verbose=1, sample_weight=None)

Computes the loss on some input data, batch by batch.

Arguments

  • x: input data, as a Numpy array or list of Numpy arrays (if the model has multiple inputs).
  • y: labels, as a Numpy array.
  • batch_size: integer. Number of samples per gradient update.
  • verbose: verbosity mode, 0 or 1.
  • sample_weight: sample weights, as a Numpy array.

Returns

Scalar test loss (if the model has no metrics) or list of scalars (if the model computes other metrics). The attribute model.metrics_names will give you the display labels for the scalar outputs.

predict

predict(self, x, batch_size=32, verbose=0)

Generates output predictions for the input samples, processing the samples in a batched way.

Arguments

  • x: the input data, as a Numpy array.
  • batch_size: integer.
  • verbose: verbosity mode, 0 or 1.

Returns

A Numpy array of predictions.

predict_classes

predict_classes(self, x, batch_size=32, verbose=1)

Generate class predictions for the input samples batch by batch.

Arguments

  • x: input data, as a Numpy array or list of Numpy arrays (if the model has multiple inputs).
  • batch_size: integer.
  • verbose: verbosity mode, 0 or 1.

Returns

A numpy array of class predictions.

predict_proba

predict_proba(self, x, batch_size=32, verbose=1)

Generates class probability predictions for the input samples batch by batch.

Arguments

  • x: input data, as a Numpy array or list of Numpy arrays (if the model has multiple inputs).
  • batch_size: integer.
  • verbose: verbosity mode, 0 or 1.

Returns

A Numpy array of probability predictions.

train_on_batch

train_on_batch(self, x, y, class_weight=None, sample_weight=None)

Single gradient update over one batch of samples.

Arguments

  • x: input data, as a Numpy array or list of Numpy arrays (if the model has multiple inputs).
  • y: labels, as a Numpy array.
  • class_weight: dictionary mapping classes to a weight value, used for scaling the loss function (during training only).
  • sample_weight: sample weights, as a Numpy array.

Returns

Scalar training loss (if the model has no metrics) or list of scalars (if the model computes other metrics). The attribute model.metrics_names will give you the display labels for the scalar outputs.

test_on_batch

test_on_batch(self, x, y, sample_weight=None)

Evaluates the model over a single batch of samples.

Arguments

  • x: input data, as a Numpy array or list of Numpy arrays (if the model has multiple inputs).
  • y: labels, as a Numpy array.
  • sample_weight: sample weights, as a Numpy array.

Returns

Scalar test loss (if the model has no metrics) or list of scalars (if the model computes other metrics). The attribute model.metrics_names will give you the display labels for the scalar outputs.

predict_on_batch

predict_on_batch(self, x)

Returns predictions for a single batch of samples.

fit_generator

fit_generator(self, generator, samples_per_epoch, nb_epoch, verbose=1, callbacks=[], validation_data=None, nb_val_samples=None, class_weight=None)

Fits the model on data generated batch-by-batch by a Python generator. The generator is run in parallel to the model, for efficiency. For instance, this allows you to do real-time data augmentation on images on CPU in parallel to training your model on GPU.

Arguments

  • generator: a generator. The output of the generator must be either
    • a tuple (inputs, targets)
    • a tuple (inputs, targets, sample_weights). All arrays should contain the same number of samples. The generator is expected to loop over its data indefinitely. An epoch finishes when samples_per_epoch samples have been seen by the model.
  • samples_per_epoch: integer, number of samples to process before going to the next epoch.
  • nb_epoch: integer, total number of iterations on the data.
  • verbose: verbosity mode, 0, 1, or 2.
  • callbacks: list of callbacks to be called during training.
  • validation_data: this can be either
    • a generator for the validation data
    • a tuple (inputs, targets)
    • a tuple (inputs, targets, sample_weights).
  • nb_val_samples: only relevant if validation_data is a generator. number of samples to use from validation generator at the end of every epoch.
  • class_weight: dictionary mapping class indices to a weight for the class.

Returns

A History object.

Example

def generate_arrays_from_file(path):
    while 1:
    f = open(path)
    for line in f:
        # create numpy arrays of input data
        # and labels, from each line in the file
        x, y = process_line(line)
        yield (x, y)
    f.close()

model.fit_generator(generate_arrays_from_file('/my_file.txt'),
        samples_per_epoch=10000, nb_epoch=10)

evaluate_generator

evaluate_generator(self, generator, val_samples)

Evaluates the model on a data generator. The generator should return the same kind of data as accepted by test_on_batch.

  • Arguments:
  • generator: generator yielding tuples (inputs, targets) or (inputs, targets, sample_weights)
  • val_samples: total number of samples to generate from generator before returning.