pip error while installing package in Cygwin/Python2.7

You can't just "run rebaseall" the way the site you link to implies. You need to do the following:

1. Exit all running Cygwin programs. Yes, all of them, even your shell, even MinTTY, even X11.
2. Start > Run > C:\cygwin\bin\ash.exe > OK.
3. cd /bin
4. Type ./rebaseall and press Return.
5. That may take a few minutes. Go get a coffee.
6. Come back, try again.

I've no idea how apt-cyg works, but it appears to use the standard Cygwin repositories. Unless you have very good reason to do otherwise, I'd use the standard Cygwin setup.exe installer for all your install/upgrade/whatever needs, as it does a pretty good job of doing all your rebasing for you.

In particular, if the above steps don't work, I'd uninstall Python with apt-cyg, and try again by installing it with the standard installer. You can download it again from cygwin.com if you need to.

Try simply running export temp= from the cygwin console. It solved the issue for me.