How to solve the problem of ImportError: cannot import name cffirmware

[Clint-L]

setting /run_id to 93c5d544-aa5f-11ef-b97e-000c29926b5b
process[rosout-1]: started with pid [52941]
started core service [/rosout]
process[crazyswarm_ros-2]: started with pid [52948]
Traceback (most recent call last):
File "/home/clint/swarm_simulator_ws/devel/lib/crazyswarm_ros/crazyswarm_sim.py", line 15, in
exec(compile(fh.read(), python_script, 'exec'), context)
File "/home/clint/swarm_simulator_ws/src/crazyswarm_ros/scripts/crazyswarm_sim.py", line 26, in
main()
File "/home/clint/swarm_simulator_ws/src/crazyswarm_ros/scripts/crazyswarm_sim.py", line 17, in main
swarm = Crazyswarm()
File "crazyswarm_py.py", line 47, in pycrazyswarm.crazyswarm_py.Crazyswarm.init
File "crazyflieSim.py", line 8, in init pycrazyswarm.crazyflieSim
ImportError: cannot import name cffirmware
[crazyswarm_ros-2] process has died [pid 52948, exit code 1, cmd /home/clint/swarm_simulator_ws/devel/lib/crazyswarm_ros/crazyswarm_sim.py __name:=crazyswarm_ros __log:=/home/clint/.ros/log/93c5d544-aa5f-11ef-b97e-000c29926b5b/crazyswarm_ros-2.log].
log file: /home/clint/.ros/log/93c5d544-aa5f-11ef-b97e-000c29926b5b/crazyswarm_ros-2*.log