Can't import dash_core_components

I installed dash on ubuntu 18.04:
pip3 install dash

Then I have a test program,, and I get the following error. What is wrong?

import os, pandas as pd
import plotly
import dash
import dash_core_components as dcc <<<<<<<<<<<<< error here:
Exception has occurred:SystemExit
File "…/, line 4, in
import dash_core_components as dcc
File "…/, line 3, in
import dash

Are you sure dash core components was installed with Dash?

It turned out that the problem was that my test program was named ‘’. That is bad. I renamed it to and now it works.