NameError: name 'mujoco_env' is not defined

[xiaohythu]

when I run the example.py with "

python example.py

"
A following error occured:

No module named 'clevr_robot_env'
Traceback (most recent call last):
File "example.py", line 25, in
from env import ClevrEnv
File "/home/rll/xiaohouyuan/clevr_robot_env-master/env.py", line 86, in
class ClevrEnv(mujoco_env.MujocoEnv, utils.EzPickle):
NameError: name 'mujoco_env' is not defined