After upgrading to pip 10 on Linux, many users are encountering variations of the error
ImportError: cannot import name 'main'. These are caused by an incorrect attempt to upgrade pip, which has typically resulted in (parts of) multiple versions of pip being installed in the same Python installation, and those parts being incompatible.
It should be noted that these issues are invariably not problems with pip itself, but are due to incorrect use of pip, or unexpected interactions with system scripts that are not controlled by pip. So while we'll try to help you solve your issue, this is not the "fault" of pip, and you will have to be prepared to do at least some of the debugging and fixes on your own.
First, some general advice. It is assumed that anyone encountering issues will have failed to follow some part of this advice. Listing these items here is not intended to imply that "it's your fault and we won't help", but rather to help users to identify what went wrong, so