Fix #77 - Stop throwing exceptions if $WINDOWID has not been set.

[pmav99]

Traceback (most recent call last):                                                                                                                                                                                 
  File "/usr/bin/ntfy", line 11, in <module>
    load_entry_point('ntfy==2.4.1', 'console_scripts', 'ntfy')()
  File "/usr/lib/python3.6/site-packages/ntfy/cli.py", line 341, in main
    message, retcode = args.func(args)
  File "/usr/lib/python3.6/site-packages/ntfy/cli.py", line 64, in run_cmd
    if args.unfocused_only and is_focused():
  File "/usr/lib/python3.6/site-packages/ntfy/terminal.py", line 61, in is_focused
    return linux_window_is_focused()
  File "/usr/lib/python3.6/site-packages/ntfy/terminal.py", line 15, in linux_window_is_focused
    return int(environ['WINDOWID']) == window_id
  File "/usr/lib/python3.6/os.py", line 669, in __getitem__
    raise KeyError(key) from None
KeyError: 'WINDOWID'

The KeyError comes from the usage of environ["WINDOWID"]. What should be used instead is the get method, e.g. environ.get("WINDOWID") which return None if the key is missing. Of course None is also a non-valid argument for int() but I think that defaulting to 0 is reasonable.

[coveralls]

Coverage decreased (-0.3%) to 87.5% when pulling cb0b11d on pmav99:issue-77 into 6ab15e0 on dschep:master.

[coveralls]

Coverage decreased (-0.3%) to 87.5% when pulling cb0b11d on pmav99:issue-77 into 6ab15e0 on dschep:master.

[pmav99]

Travis builds for python 3.3 and 3.4 are failing but the failures seem to be unrelated with the code changes.

[dschep]

Any particular reason for using shlex and splitting a str command instead of defining it as a list to begin with?

[pmav99]

shlex.split("xprop -root _NET_ACTIVE_WINDOW")
# vs
['xprop', '-root', '\t$0', '_NET_ACTIVE_WINDOW']

IMHO, shlex has the following advantages:

• It is more readable: less visual clutter (quotes and commas), especially if you have a long command.
• It is more easily testable: just copy paste the command and run it on your shell.

All in all I believe that using shlex is a better practice in general and I use it on my own code, but this is not my repo, so if you prefer a list, a list it shall be :)

[dschep]

Makes sense to me 👍

[dschep]

Switch " use to ' and I'm happy with this change (I should probably make the linter enforce that rule 😁)

[coveralls]

Coverage decreased (-0.3%) to 87.5% when pulling 5c2128e on pmav99:issue-77 into 6ab15e0 on dschep:master.

[coveralls]

Coverage decreased (-0.3%) to 87.5% when pulling 5c2128e on pmav99:issue-77 into 6ab15e0 on dschep:master.

[pmav99]

I rebased.

BTW, I think that get_tty() is not being used anywhere and it should probably be removed.