When I try to learn ML using tensorflow and keras, I came across callbacks.py, in which some functions are defined with out anything inside and it's still legal no error reported. May I know why?
@keras_export('keras.callbacks.Callback')
class Callback(object):
"""Abstract base class used to build new callbacks.
Attributes:
params: dict. Training parameters
(eg. verbosity, batch size, number of epochs...).
model: instance of `keras.models.Model`.
Reference of the model being trained.
validation_data: Deprecated. Do not use.
The `logs` dictionary that callback methods
take as argument will contain keys for quantities relevant to
the current batch or epoch.
Currently, the `.fit()` method of the `Model` class
will include the following quantities in the `logs` that
it passes to its callbacks:
on_epoch_end: logs include `acc` and `loss`, and
optionally include `val_loss`
(if validation is enabled in `fit`), and `val_acc`
(if validation and accuracy monitoring are enabled).
on_batch_begin: logs include `size`,
the number of samples in the current batch.
on_batch_end: logs include `loss`, and optionally `acc`
(if accuracy monitoring is enabled).
"""
def __init__(self):
self.validation_data = None
self.model = None
# Whether this Callback should only run on the chief worker in a
# Multi-Worker setting.
# TODO(omalleyt): Make this attr public once solution is stable.
self._chief_worker_only = None
def set_params(self, params):
self.params = params
def set_model(self, model):
self.model = model
def on_batch_begin(self, batch, logs=None):
"""A backwards compatibility alias for `on_train_batch_begin`."""
def on_batch_end(self, batch, logs=None):
"""A backwards compatibility alias for `on_train_batch_end`."""
