Have you met similar issue with tools/install_venv.py script?

Firstly, please allow me to give my acknowledgement to nova developers for providing install_venv.py script to set up the development environment for nova. It really gives me a lot of help to better understand nova's dependencies.
However, I am not sure whether it is due to the problem of my local network connection. Each time I run python tools/install_venv.py, I always get a failure because one package(it could be anyone) within pip-requires failed to download or install. No matter how many times I tried, there is no single success for me.
Then, I tried to split all the packages within pip-requires by converting them into a set of commands one by one. For example, there is amqplib==0.6.1, then I will get a command sudo tools/with_venv.sh pip install amqplib==0.6.1...
When I run these commands one by one, the packages can be successfully installed.
After it, I run install_venv.py, then I will have virtualenv successfully installed.
I was wondering if anyone of you has got similar issues. Is it due to the local network connection? Do you think it is an issue for us to fix it in the script code?