Lots of other threads about similar issues, but none that I could find where quite the same case as mine. So, here goes:
Things I did:
Got this error after recently (summer 2017) updating Homebrew and python. The issue in my case was that Homebrew no longer overwrites the system python and I didn't have virtualenv and virtualenvwrapper installed for the system python.
The solution in my case was to add the following to ~/.bash_profile (or ~/.zshrc):
export PATH="$(brew --prefix)/opt/python/libexec/bin:$PATH"
This made python point to the brew version of python and also gave me pip back. This version of python had virtualenv and virtualenvwrapper installed so the error no longer appeared. See the caveats section under brew info python and https://github.com/Homebrew/homebrew-core/issues/15746 for more information