AttributeError: module 'tensorflow' has no attribute 'get_default

やりたいこと

vgg16で転移学習さそうとしているのですがどのサイトを見てもこのエラーの解消ができません。

ソースコード

from keras.models import Model
from keras.layers import Dense, GlobalAveragePooling2D,Input
from keras.applications.vgg16 import VGG16
from keras.preprocessing.image import ImageDataGenerator
import matplotlib.pyplot as plt


N_CATEGORIES = 2
IMAGE_SIZE = 224
BATCH_SIZE = 5
NUM_EPOCHS = 5
0
train_data_dir = 'C:/Users/s/reserch/Cup'
validation_data_dir = 'C:/Users/s/reserch/Cup'

NUM_TRAINING = 30
NUM_VALIDATION = 5

input_tensor = Input(shape=(IMAGE_SIZE, IMAGE_SIZE, 3))
base_model = VGG16(weights='imagenet', include_top=False, input_tensor=input_tensor)

x = base_model.output
x = GlobalAveragePooling2D()(x)
x = Dense(1024, activation='relu')(x)
predictions = Dense(N_CATEGORIES, activation='softmax')(x)
model = Model(inputs=base_model.input, outputs=predictions)

# for layer in base_model.layers:
for layer in base_model.layers[:15]:
   layer.trainable = False
from keras.optimizers import SGD
model.compile(optimizer=SGD(lr=0.0001, momentum=0.9), loss='categorical_crossentropy',metrics=['accuracy'])

model.summary()


train_datagen = ImageDataGenerator(
   rescale=1.0 / 255,
   shear_range=0.2,
   zoom_range=0.2,
   horizontal_flip=True,
   rotation_range=10)
test_datagen = ImageDataGenerator(
   rescale=1.0 / 255,
)

train_generator = train_datagen.flow_from_directory(
   train_data_dir,
   target_size=(IMAGE_SIZE, IMAGE_SIZE),
   batch_size=BATCH_SIZE,
   class_mode='categorical',
   shuffle=True
)

validation_generator = test_datagen.flow_from_directory(
   validation_data_dir,
   target_size=(IMAGE_SIZE, IMAGE_SIZE),
   batch_size=BATCH_SIZE,
   class_mode='categorical',
   shuffle=True
)
history = model.fit_generator(train_generator,
   steps_per_epoch=NUM_TRAINING//BATCH_SIZE,
   epochs=NUM_EPOCHS,
   verbose=1,
   validation_data=validation_generator,
   validation_steps=NUM_VALIDATION//BATCH_SIZE,
   )
model.save('transfer.h5')  # モデルの保存