In case you are experiencing high latency and delay in a Python ROS subscriber used for real-time applications, we might have the solution for you. In many of our applications we experienced an increasing latency, despite having a queue of 1 selected. This goes back to this discussion.
Clone this repository on branch dev into your workspace and build your package as regular. As your package should have a run dependency on rospy, ros_comm and rospy should also automatically be built.
After sourcing of your workspace, the latency should go down to the actual time spent in the callback, instead of accumulating delay over time.
We in particular encountered this issue when having computationally-heavy code running inside the callback, such as neural network inference or similar.