How to call a method as a custom callback in Keras? - tensorflow

Question

I need to run the following method after every 5K iterations.
def evaluation_matrix(path_true,path_pred):
print(path_true,"\n",path_pred)
true_list_new, pred_list_new = read_from_folder(path_true = path_true , path_pred = path_pred)
try:
scikit_metrix(true_list_new = true_list_new,pred_list_new = pred_list_new)
except:
print("An exception occurred")
I'm hoping to use it as a callback in model.fit_generator function. How to achive this? That is parameter passing + 5K interval?
history = model.fit_generator(generator = myGene, steps_per_epoch=steps_per_epoch, epochs=epoch, verbose = 1, callbacks=[],shuffle=True)

Answer 1

A custom callback is a powerful tool to customize the behavior of a Keras model during training, evaluation, or inference.
Below is an example where we are calculating gradient after every epochs. Similarly you can do more customize with many inbuilt methods. You can find more about it here - https://www.tensorflow.org/guide/keras/custom_callback
Note: I was using tensorflow 1.15.0
# (1) Importing dependency
import tensorflow as tf
import keras
from keras import backend as K
from keras.models import Sequential
from keras.layers import Dense, Activation, Dropout, Flatten, Conv2D, MaxPooling2D
from keras.layers.normalization import BatchNormalization
import numpy as np
np.random.seed(1000)
# (2) Get Data
import tflearn.datasets.oxflower17 as oxflower17
x, y = oxflower17.load_data(one_hot=True)
# (3) Create a sequential model
model = Sequential()
# 1st Convolutional Layer
model.add(Conv2D(filters=96, input_shape=(224,224,3), kernel_size=(11,11), strides=(4,4), padding='valid'))
model.add(Activation('relu'))
# Pooling
model.add(MaxPooling2D(pool_size=(2,2), strides=(2,2), padding='valid'))
# Batch Normalisation before passing it to the next layer
model.add(BatchNormalization())
# 2nd Convolutional Layer
model.add(Conv2D(filters=256, kernel_size=(11,11), strides=(1,1), padding='valid'))
model.add(Activation('relu'))
# Pooling
model.add(MaxPooling2D(pool_size=(2,2), strides=(2,2), padding='valid'))
# Batch Normalisation
model.add(BatchNormalization())
# 3rd Convolutional Layer
model.add(Conv2D(filters=384, kernel_size=(3,3), strides=(1,1), padding='valid'))
model.add(Activation('relu'))
# Batch Normalisation
model.add(BatchNormalization())
# 4th Convolutional Layer
model.add(Conv2D(filters=384, kernel_size=(3,3), strides=(1,1), padding='valid'))
model.add(Activation('relu'))
# Batch Normalisation
model.add(BatchNormalization())
# 5th Convolutional Layer
model.add(Conv2D(filters=256, kernel_size=(3,3), strides=(1,1), padding='valid'))
model.add(Activation('relu'))
# Pooling
model.add(MaxPooling2D(pool_size=(2,2), strides=(2,2), padding='valid'))
# Batch Normalisation
model.add(BatchNormalization())
# Passing it to a dense layer
model.add(Flatten())
# 1st Dense Layer
model.add(Dense(4096, input_shape=(224*224*3,)))
model.add(Activation('relu'))
# Add Dropout to prevent overfitting
model.add(Dropout(0.4))
# Batch Normalisation
model.add(BatchNormalization())
# 2nd Dense Layer
model.add(Dense(4096))
model.add(Activation('relu'))
# Add Dropout
model.add(Dropout(0.4))
# Batch Normalisation
model.add(BatchNormalization())
# 3rd Dense Layer
model.add(Dense(1000))
model.add(Activation('relu'))
# Add Dropout
model.add(Dropout(0.4))
# Batch Normalisation
model.add(BatchNormalization())
# Output Layer
model.add(Dense(17))
model.add(Activation('softmax'))
model.summary()
# (4) Compile
model.compile(loss='categorical_crossentropy', optimizer='adam', metrics=['accuracy'])
epoch_gradient = []
# Define the Required Callback Function
class GradientCalcCallback(tf.keras.callbacks.Callback):
def get_gradient_func(model):
grads = K.gradients(model.total_loss, model.trainable_weights)
inputs = model.model._feed_inputs + model.model._feed_targets + model.model._feed_sample_weights
func = K.function(inputs, grads)
return func
def on_epoch_end(self, epoch, logs=None):
get_gradient = get_gradient_func(model)
grads = get_gradient([x, y, np.ones(len(y))])
epoch_gradient.append(grads)
model.fit(x, y, batch_size=64, epochs= 4, verbose=1, validation_split=0.2, shuffle=True, callbacks=[GradientCalcCallback()])
# (7) Convert to a 2 dimensiaonal array of (epoch, gradients) type
gradient = np.asarray(epoch_gradient)
print("Total number of epochs run:", epoch)
print("Gradient Array has the shape:",gradient.shape)