Fix error when TERM is unset or improperly set

[jgkamat]

Closes #39.

This is an alternative, simpler solution than merging the blessed-integration branch, because that seems stalled.

If TERM is unset, we should default to a dumb term, as we cannot be sure colors are supported, which matches the behavior of less, for example.

If there is an error reading the TERM variable, we should fall back to not outputing any color, which mimics less again.

I tried to write some simple tests for this but the results seem to be cached, even across Terminal instances? Is this happening somehow, and is there a way to disable the cache?

[erikrose]

There's a longstanding bug in CPython which causes only the first call to setupterm() in a process to actually do anything. That's what the elaborate test refactor in blessed works around.

[erikrose]

Thanks for the patch! I'm mostly just concerned with the bare except, but if you can illuminate me on the other question, so much the better.

[erikrose]

Can we tighten this up to catch only the expected sorts of errors?

[jgkamat]

ah, I was worried that the exception thrown (_curses.error) was private, but I think I can catch it with curses.error which is documented.

[erikrose]

Does 'dumb' help, over how 'unknown' used to behave? I honestly can't figure out why I put 'unknown' in there in the first place.

[jgkamat]

for me at least, unknown isn't a valid terminal in my term-info and causes a crash as well (which is caught in the except, but I'd rather avoid that if possible). While we can't guarantee that dumb will exist either, I think it has a much higher chance of working (as it's defined on pretty much everything).

[erikrose]

Thank you! Mozilla's build system, for one, will be happy. :-)

[Whissi]

This fix is not enough. When TERM is explicit set to "" (nothing, e.g. TERM=), blessings is still failing:

error: must call (at least) setupterm() first

  File "/var/tmp/portage/www-client/firefox-60.2.0/work/firefox-60.2.0/python/mach/mach/main.py", line 359, in run
    return self._run(argv)
  File "/var/tmp/portage/www-client/firefox-60.2.0/work/firefox-60.2.0/python/mach/mach/main.py", line 448, in _run
    write_times=write_times)
  File "/var/tmp/portage/www-client/firefox-60.2.0/work/firefox-60.2.0/python/mach/mach/logging.py", line 214, in add_terminal_logging
    formatter.set_terminal(self.terminal)
  File "/var/tmp/portage/www-client/firefox-60.2.0/work/firefox-60.2.0/python/mach/mach/logging.py", line 96, in set_terminal
    self._sgr0 = blessings.tigetstr('sgr0') or '' if terminal and blessings else ''