Error

---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-38-b165647910bb> in <module>
     13 with rosbag.Bag('images.bag', 'r') as image_bag:
     14     for topic, image_message, t in image_bag.read_messages():
---> 15         cv_image = bridge.imgmsg_to_cv2(image_message, "bgr8")
     16         cv2.imshow("image", cv_image)
     17         break

/opt/ros/melodic/lib/python2.7/dist-packages/cv_bridge/core.py in imgmsg_to_cv2(self, img_msg, desired_encoding)
    161         import cv2
    162         import numpy as np
--> 163         dtype, n_channels = self.encoding_to_dtype_with_channels(img_msg.encoding)
    164         dtype = np.dtype(dtype)
    165         dtype = dtype.newbyteorder('>' if img_msg.is_bigendian else '<')

/opt/ros/melodic/lib/python2.7/dist-packages/cv_bridge/core.py in encoding_to_dtype_with_channels(self, encoding)
     97
     98     def encoding_to_dtype_with_channels(self, encoding):
---> 99         return self.cvtype2_to_dtype_with_channels(self.encoding_to_cvtype2(encoding))
    100
    101     def compressed_imgmsg_to_cv2(self, cmprs_img_msg, desired_encoding = "passthrough"):

/opt/ros/melodic/lib/python2.7/dist-packages/cv_bridge/core.py in encoding_to_cvtype2(self, encoding)
     89
     90     def encoding_to_cvtype2(self, encoding):
---> 91         from cv_bridge.boost.cv_bridge_boost import getCvType
     92
     93         try:

ImportError: dynamic module does not define module export function (PyInit_cv_bridge_boost)