Transfer learning Error

[MaduJoe]

when I tried to section 2. Re-training Automation Tool
I got error like below :
Traceback (most recent call last):
File "object_detection/train.py", line 47, in
import tensorflow as tf
ImportError: No module named tensorflow

My docker environment : Ubuntu 16.04.05 LTS , TF - 1.18.0 , Python - 3.5.2
Could you let me know why this happened ?