Python '；非类型'；对象没有属性'；数据类型'；-热图函数问题

我正在尝试为黑白图像制作GradCam热图。我已经成功地定义了一个函数，它将获取一个图像的路径，并为它创建一个热图。我一定是做错了什么，因为我犯了个错误

AttributeError                            Traceback (most recent call last)
<ipython-input-34-f75f6e449e46> in <module>()
      1 img_path2 = "/content/CBIS_DDSM/png_images/calc_case_description_train_set/Calc-Training_P_00005_RIGHT_CC_1-1.3.6.1.4.1.9590.100.1.2.328778919012412769218080124214088709081-1.3.6.1.4.1.9590.100.1.2.393344010211719049419601138200355094682-000001.NOTHING-base_top.png"
      2 
----> 3 get_class_activation_map(img_path2)

1 frames
/tensorflow-1.15.2/python3.7/keras/backend/tensorflow_backend.py in mean(x, axis, keepdims)
   1808     {{np_implementation}}
   1809     """
-> 1810     if x.dtype.base_dtype == tf.bool:
   1811         x = tf.cast(x, floatx())
   1812     return tf.reduce_mean(x, axis, keepdims)

AttributeError: 'NoneType' object has no attribute 'dtype'

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get\u class\u activation\u map（）

函数中的确切位置的信息。

def get_class_activation_map(path) :
    
    img_path =  path 
    img = cv2.imread(img_path)
    img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    img = cv2.resize(img, (150, 150))
    img = np.expand_dims(img,axis=0)
    img = np.expand_dims(img,axis=1)

    img = np.moveaxis(img, 0, -1)
    predict = model.predict(img)
    target_class = np.argmax(predict[0])
    last_conv = model.get_layer('densenet121')
    grads =K.gradients(model.output[:,target_class],last_conv.output)[0]
    pooled_grads = K.mean(grads,axis=(0,1,2))
    iterate = K.function([model.input],[pooled_grads,last_conv.output[0]])
    pooled_grads_value,conv_layer_output = iterate([img])
    
    for i in range(512):
        conv_layer_output[:,:,i] *= pooled_grads_value[i]
    
    heatmap = np.mean(conv_layer_output,axis=-1)
    
    for x in range(heatmap.shape[0]):
        for y in range(heatmap.shape[1]):
            heatmap[x,y] = np.max(heatmap[x,y],0)
    heatmap = np.maximum(heatmap,0)
    heatmap /= np.max(heatmap)
    im = plt.imshow(heatmap)
    return im