Unescaped space in proxy URL causes "Failed to parse" error in pip 19.2.1

[davidedb]

Environment

• Pip version: 19.2.1
• Python version: 3.6.3 and 2.7.4
• Operating system: RHELS 6.9

Description
After upgrading pip from version 19.1.1 to 19.2.1, I was not able anymore to install any package.
For example, the command pip install upydev terminates immediately with the error message:

ERROR: Could not install packages due to an EnvironmentError: Failed to parse: http://name surname:password@proxy:8080

After some debugging I found out the problem is generated by the presence of a space character in the user login, i.e. between the user name and his surname.

Workaround
Simply replacing the space with the corresponding URL-encoded entity solves the issue.

setenv HTTP_PROXY 'http://name%20surname:password@proxy:8080`
pip install upydev

[pradyunsg]

Thanks for filing this issue @davidedb!

pip's URL authentication handling has become stricter in pip 19.2. This has been brought up in #6775. I would appreciate if you could chime in there, about how it can be made easier to debug this issue for end users.

I'll close this as a duplicate of #6775.