root@c9c8c4b7bc54:/ews# pip install pytz
Requirement already satisfied: pytz in /usr/local/lib/python3.7/site-packages (2019.3)

root@c9c8c4b7bc54:/ews# ./ews-fetch-calendar.py
Traceback (most recent call last):
  File "./ews-fetch-calendar.py", line 12, in <module>
    from pytz import timezone
ImportError: No module named pytz