sugar-emulator: better error message if X server is unreachable

[sascha_silbe]

Seems I didn't test the error case of not being able to connect to the X server at all. Reported by yevlempy on sugar-devel:

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?

Xephyr cannot open host display. Is DISPLAY set?
xrdb: No such file or directory
xrdb: Can't open display ':39'
Window manager error: Unable to open X display :39
1267079814.2631569 STARTUP: Starting the shell
Traceback (most recent call last):
  File "/home/Rinki/project/sugar-jhbuild/install/bin/sugar-session", line 32, in <module>
    import gtk
  File "/usr/lib/python2.6/site-packages/gtk-2.0/gtk/__init__.py", line 64, in <module>
    _init()
  File "/usr/lib/python2.6/site-packages/gtk-2.0/gtk/__init__.py", line 52, in _init
    _gtk.init_check()
RuntimeError: could not open display
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/Rinki/project/sugar-jhbuild/install/lib/python2.6/site-packages/jarabe/util/emulator.py", line 156, in main
    _kill_pipe(server)
  File "/home/Rinki/project/sugar-jhbuild/install/lib/python2.6/site-packages/jarabe/util/emulator.py", line 80, in _kill_pipe
    os.kill(pipe.pid, signal.SIGTERM)
AttributeError: 'NoneType' object has no attribute 'pid'

[erikos]

No show stopper.

[tomeu]

+ sys.stderr.write('Error executing server: %s\n' % (exc, ))

Better print the full exception including the traceback? If cannot use logging.error, then see in  http://docs.python.org/library/traceback.html .

+ if not pipe:
+ if not server:

Always use "is None", classes implementing a collection protocol evaluate to False when empty.

[sascha_silbe]

sugar-emulator: better error messages in case of failures

[sascha_silbe]

Replying to tomeu:

+ sys.stderr.write('Error executing server: %s\n' % (exc, ))
Better print the full exception including the traceback?

That will add no useful information and instead confuse the user.

+ if not pipe:
+ if not server:
Always use "is None", classes implementing a collection protocol evaluate to False when empty.

Changed.

[tomeu]

Replying to sascha_silbe:

Replying to tomeu:

+ sys.stderr.write('Error executing server: %s\n' % (exc, ))
Better print the full exception including the traceback?

That will add no useful information and instead confuse the user.

I don't agree with this, asked in the ml for opinions.

[tomeu]

Replying to tomeu:

Replying to sascha_silbe:

Replying to tomeu:

+ sys.stderr.write('Error executing server: %s\n' % (exc, ))
Better print the full exception including the traceback?

That will add no useful information and instead confuse the user.

I don't agree with this, asked in the ml for opinions.

Not such a big deal, pushed as  http://git.sugarlabs.org/projects/sugar/repos/mainline/commits/cb4fdde40a5

[sascha_silbe]

Thanks!