Error：The shape of the input to Flatten is not fully defined got None, None, 120 .

 报错：

错误位置：

Flatten()

错误原因：

没有明确的规定输入的shape

解决方法：

输入模型时明确尺寸

e.g.   vgg16 = keras.applications.vgg16.VGG16(include_top=False, weights='imagenet', input_shape=(224, 224, 3))
x = vgg16.output
x = Flatten()(x)