ModuleNotFoundError: No module named 'pymssql

I imported the following modules:

import sqlalchemy
from sqlalchemy import create_engine, text, exc
from sqlalchemy.dialects.mssql import pymssql

Set-up a connection to SQL Server

engine = sqlalchemy.create_engine('mssql+pymssql://localhost\\SQLEXPRESS/NORTHWND?trusted_connection=yes')
conn = engine.connect()

I get the following error: 

module = __import__('pymssql')
ModuleNotFoundError: No module named 'pymssql'

I looked at the folder listed in the error msg (C:\Python36\lib\site-packages\sqlalchemy\dialects\mssql\pymssql.py)

The file is there?? 

Any suggestions appreciated.