Comment 6 for bug 1486731

I have the same problem on my debian sid install. When I installed hplip I had to switch to root to install it as otherwise the spinning bar would spin forever after asking my password. Unfortunately hp-plugin cannot be run as root so I have the spinning bar issue here. I think it's a problem when trying to call su.

Here is what my terminal prints:
HP Linux Imaging and Printing System (ver. 3.15.9)
Plugin Download and Install Utility ver. 2.1

Copyright (c) 2001-15 Hewlett-Packard Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

HP Linux Imaging and Printing System (ver. 3.15.9)
Plugin Download and Install Utility ver. 2.1

Copyright (c) 2001-15 Hewlett-Packard Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Checking for network connection...
Downloading plug-in from:
Receiving digital keys: /usr/bin/gpg --homedir /home/alejandro/.hplip/.gnupg --no-permission-warning --keyserver pgp.mit.edu --recv-keys 0x4ABA2F66DBD5A95894910E0673D770CDA59047B9
Creating directory plugin_tmp
Verifying archive integrity... All good.
Uncompressing HPLIP 3.15.9 Plugin Self Extracting Archive............................................

HP Linux Imaging and Printing System (ver. 3.15.9)
Plugin Installer ver. 3.0

Copyright (c) 2001-15 Hewlett-Packard Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Plug-in version: 3.15.9
Installed HPLIP version: 3.15.9
Number of files to install: 38

 - <---- spinning wheel spins forever

^CTraceback (most recent call last):
  File "./plugin_install.py", line 249, in <module>
    ok = installPlugin()
  File "./plugin_install.py", line 56, in installPlugin
    status, output = utils.run(cmd, passwordObj)
  File "/usr/share/hplip/base/utils.py", line 1275, in run
    i = child.expect(EXPECT_LIST)
  File "/usr/share/hplip/base/pexpect/__init__.py", line 1418, in expect
    timeout, searchwindowsize)
  File "/usr/share/hplip/base/pexpect/__init__.py", line 1433, in expect_list
    timeout, searchwindowsize)
  File "/usr/share/hplip/base/pexpect/__init__.py", line 1502, in expect_loop
    c = self.read_nonblocking(self.maxread, timeout)
  File "/usr/share/hplip/base/pexpect/__init__.py", line 901, in read_nonblocking
    r, w, e = self.__select([self.child_fd], [], [], timeout)
  File "/usr/share/hplip/base/pexpect/__init__.py", line 1687, in __select
    return select.select(iwtd, owtd, ewtd, timeout)
KeyboardInterrupt
error: Python gobject/dbus may be not installed
error: Plug-in install failed.

Done.