psycopg2 code completion does not work

I am using Pycharm as the below version on ubuntu 18.04. and install psycopg2 from pip.

PyCharm 2018.2.5 (Community Edition)
Build #PC-182.5107.22, built on November 13, 2018
JRE: 1.8.0_152-release-1248-b22 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.ot
Linux 4.15.0-39-generic

import psycopg2
cn = psycopg2.connect

On the above code, code completion works well.

However, The below code, code completion does not work. Could someone let me know how to work my code completion work well ?

cur = cn.cursol

Regards,