message_filter (Python 3) not working in ROS Melodic

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System information

• OS: Ubuntu 18.04
• ROS version: Melodic
• Conda environment: python=3.7 (Needed for a python3 processing module)

Problem explanation

I try to create a message filter that subscribes to two sensor_msg topics after which a python3 module processes the Color and depth data in a callback function. To do this, I created the following script to achieve this:

#!/usr/bin/env python3

## Import standard library packages ##
import sys

## Import ROS python packages ##
import rospy
import sensor_msgs
from message_filters import ApproximateTimeSynchronizer, Subscriber

def gotimage(image, camerainfo):
    assert image.header.stamp == camerainfo.header.stamp
    print("got an Image and CameraInfo")

## Main script ##
# Only runs when this script is executed directly
if __name__ == "__main__":

    ## Initialize ros node ##
    rospy.init_node('grasp_planner', anonymous=True)
    image_sub = Subscriber("/kinect2/hd/image_color", sensor_msgs.msg.Image)
    camera_sub = Subscriber("/kinect2/hd/camera_info", sensor_msgs.msg.CameraInfo)

    ## Create message_filter ##
    ats = ApproximateTimeSynchronizer([image_sub, camera_sub], queue_size=5, slop=0.1)
    ats.registerCallback(gotimage)
    rospy.spin()

Unfortunately, after trying to run this script, I get the following error message:

/home/ricks/miniconda3/envs/panda_autograsp/lib/python3.7/site-packages/tensorflow/python/framework/dtypes.py:526: FutureWarning: Passing (type, 1) or '1type' as a synonym of type is deprecated; in a future version of numpy, it will be understood as (type, (1,)) / '(1,)type'.
  _np_qint8 = np.dtype([("qint8", np.int8, 1)])
/home/ricks/miniconda3/envs/panda_autograsp/lib/python3.7/site-packages/tensorflow/python/framework/dtypes.py:527: FutureWarning: Passing (type, 1) or '1type' as a synonym of type is deprecated; in a future version of numpy, it will be understood as (type, (1,)) / '(1,)type'.
  _np_quint8 = np.dtype([("quint8", np.uint8, 1)])
/home/ricks/miniconda3/envs/panda_autograsp/lib/python3.7/site-packages/tensorflow/python/framework/dtypes.py:528: FutureWarning: Passing (type, 1) or '1type' as a synonym of type is deprecated; in a future version of numpy, it will be understood as (type, (1,)) / '(1,)type'.
  _np_qint16 = np.dtype([("qint16", np.int16, 1)])
/home/ricks/miniconda3/envs/panda_autograsp/lib/python3.7/site-packages/tensorflow/python/framework/dtypes.py:529: FutureWarning: Passing (type, 1) or '1type' as a synonym of type is deprecated; in a future version of numpy, it will be understood as (type, (1,)) / '(1,)type'.
  _np_quint16 = np.dtype([("quint16", np.uint16, 1)])
/home/ricks/miniconda3/envs/panda_autograsp/lib/python3.7/site-packages/tensorflow/python/framework/dtypes.py:530: FutureWarning: Passing (type, 1) or '1type' as a synonym of type is deprecated; in a future version of numpy, it will be understood as (type, (1,)) / '(1,)type'.
  _np_qint32 = np.dtype([("qint32", np.int32, 1)])
/home/ricks/miniconda3/envs/panda_autograsp/lib/python3.7/site-packages/tensorflow/python/framework/dtypes.py:535: FutureWarning: Passing (type, 1) or '1type' as a synonym of type is deprecated; in a future version of numpy, it will be understood as (type, (1,)) / '(1,)type'.
  np_resource = np.dtype([("resource", np.ubyte, 1)])
[ERROR] [1566834367.342856]: bad callback: <bound method Subscriber.callback of <message_filters.Subscriber object at 0x7fb849e44f50>>
Traceback (most recent call last):
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rospy/topics.py", line 750 ...