I have created a python package that includes a setup.py file. I need this package to be distributed among some clients, who will import and build their products on top of my package and I want to make the package proprietary as it contains some sensitive information. 
I have added a license header but there are some URLs that I want to hide from my clients.
How to achieve this? Thank you
You don't.  
Security through obscurity is broken from the outset.  If you ship it to the client, they own it at some level or another.
Especially in the case of python, it makes no sense to hide things, because the interpreter still has to be able to process them - if you encrypt something, you have to ship the decryption tools with it, which means a malicious user already has everything they need to figure out your secrets.
If you don't want a user to have access to it, you can't sent it to the user.  Period.
Is it possible to hide code in my importable package?