Problem with rl.memory

[PrettyMeng]

Hi there, I'm trying to reproduce your result but I got the following error:
File "train_ddpg.py", line 25, in
from rl.memory import SequentialMemory, HALGANMemory
File "/cluster/home/it_stu114/research-halgan/src/rl/memory.py", line 354, in
class HALGANMemory(PersistentMemory):
NameError: name 'PersistentMemory' is not defined

It seems that the class 'PersistentMemory' is missing.

Any help or response will be highly appreciated, thanks!