It's because in the pip configuration the index-url parameter should point to the new pypi url. Change the file in ~/.pip/pip.conf
or if you are running pip as root, in: /root/.pip/pip.conf
.
Probably you have this:
[global]
index-url=http://f.pypi.python.org/simple
You shoudl change it for this:
[global]
index-url=https://pypi.python.org/pypi/
And then all should work as before. I hope it helps you.