Treating traitsui as optional

[stewbond]

If users don't have traitsui, then GUI-specific functions now do nothing instead of crashing the application. This really helps for running unit tests on build machines without any X-server which have problems when running traitsui functions.

Note that there probably some other places where traitsui could be removed, but this at least gets the CI tests working.

Also helps with issue #70.

[corranwebster]

Have you tried running your headless tests with ETS_TOOLKIT=null environment variable set?

[stewbond]

Thanks for the response.

When I run the tests in a debian unstable chroot without python-traitsui installed, I get an ImportError [1]

When I run the tests in a debian unstable chroot with python-traitsui installed, I get Unable to access the X Display, is $DISPLAY set properly? [2]

It's also worth noting that python3-traitsui is not available in debian yet so if we did solve the $DISPLAY issue, we would still have a problem when running the tests with python3.

[1]:

export ETS_TOOLKIT=null
cd /root/python-apptools/.pybuild/cpython2_2.7_apptools/build; python2.7 -m nose -v 
apptools.io.h5.tests.test_dict_node.test_create ... ok
apptools.io.h5.tests.test_dict_node.test_is_dict_node ... ok
...
apptools.lru_cache.tests.test_lru_cache.test_cache_get ... ok
apptools.lru_cache.tests.test_lru_cache.test_updated_event ... ok
Failure: ImportError (No module named traitsui.api) ... ERROR
bind ... ok
bind with make contexts ... ok
...
test_undo_redo_1_command (apptools.undo.tests.test_command_stack.TestCommandStack) ... ok
test_undo_unnamed_command (apptools.undo.tests.test_command_stack.TestCommandStack) ... ok

======================================================================
ERROR: Failure: ImportError (No module named traitsui.api)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/nose/loader.py", line 418, in loadTestsFromName
    addr.filename, addr.module)
  File "/usr/lib/python2.7/dist-packages/nose/importer.py", line 47, in importFromPath
    return self.importFromDir(dir_path, fqname)
  File "/usr/lib/python2.7/dist-packages/nose/importer.py", line 94, in importFromDir
    mod = load_module(part_fqname, fh, filename, desc)
  File "/root/python-apptools/.pybuild/cpython2_2.7_apptools/build/apptools/naming/trait_defs/__init__.py", line 17, in <module>
    from api import *
  File "/root/python-apptools/.pybuild/cpython2_2.7_apptools/build/apptools/naming/trait_defs/api.py", line 13, in <module>
    from naming_traits import NamingInstance
  File "/root/python-apptools/.pybuild/cpython2_2.7_apptools/build/apptools/naming/trait_defs/naming_traits.py", line 25, in <module>
    from traitsui.api \
ImportError: No module named traitsui.api

----------------------------------------------------------------------
Ran 398 tests in 0.550s

FAILED (SKIP=1, errors=1)

[2]:

export ETS_TOOLKIT=null
cd /root/python-apptools/.pybuild/cpython2_2.7_apptools/build; python2.7 -m nose -v 
Unable to access the X Display, is $DISPLAY set properly?

[mdickinson]

Closing in favour of #351