Fix: Don't import all the problem builder blocks when the django app is loaded

[bradenmacdonald]

OC-1003

This fixes TNL-3563.

The pb-dashboard block was not loading due to a bizarre combination of factors, brought into play by the recent django-rest-framework upgrade.

Details:

The error was being reported as:

  File "/edx/xblocks/xblock-problem-builder/problem_builder/dashboard.py", line 415, in student_view
    value = sub_api.get_submissions(mcq_submission_key, limit=1)[0]["answer"]
AttributeError: 'NoneType' object has no attribute 'get_submissions'

To get the true error, I had to remove a try: ... except ImportError wrapper, and then we can see the real cause:

Traceback (most recent call last):
  File "manage.py", line 116, in <module>
    execute_from_command_line([sys.argv[0]] + django_args)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 443, in execute_from_command_line
    utility.execute()
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 382, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 261, in fetch_command
    klass = load_command_class(app_name, subcommand)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 69, in load_command_class
    module = import_module('%s.management.commands.%s' % (app_name, name))
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/importlib.py", line 35, in import_module
    __import__(name)
  File "/edx/app/edxapp/edx-platform/cms/djangoapps/contentstore/__init__.py", line 2, in <module>
    import contentstore.signals
  File "/edx/app/edxapp/edx-platform/cms/djangoapps/contentstore/signals.py", line 9, in <module>
    from contentstore.courseware_index import CoursewareSearchIndexer, LibrarySearchIndexer
  File "/edx/app/edxapp/edx-platform/cms/djangoapps/contentstore/courseware_index.py", line 340, in <module>
    class CoursewareSearchIndexer(SearchIndexerBase):
  File "/edx/app/edxapp/edx-platform/cms/djangoapps/contentstore/courseware_index.py", line 353, in CoursewareSearchIndexer
    UNNAMED_MODULE_NAME = _("(Unnamed)")
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/__init__.py", line 86, in ugettext
    return _trans.ugettext(message)
  File "/edx/app/edxapp/edx-platform/common/djangoapps/monkey_patch/django_utils_translation.py", line 70, in dont_translate_empty_string
    message = function(message)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 278, in ugettext
    return do_translate(message, 'ugettext')
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 268, in do_translate
    _default = translation(settings.LANGUAGE_CODE)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 183, in translation
    default_translation = _fetch(settings.LANGUAGE_CODE)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 160, in _fetch
    app = import_module(appname)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/importlib.py", line 35, in import_module
    __import__(name)
  File "/edx/app/edxapp/venvs/edxapp/src/edx-sga/edx_sga/__init__.py", line 1, in <module>
    from .sga import StaffGradedAssignmentXBlock
  File "/edx/app/edxapp/venvs/edxapp/src/edx-sga/edx_sga/sga.py", line 24, in <module>
    from submissions import api as submissions_api
  File "/edx/app/edxapp/venvs/edxapp/src/edx-submissions/submissions/api.py", line 16, in <module>
    from submissions.serializers import (
  File "/edx/app/edxapp/venvs/edxapp/src/edx-submissions/submissions/serializers.py", line 42, in <module>
    class SubmissionSerializer(serializers.ModelSerializer):
  File "/edx/app/edxapp/venvs/edxapp/src/edx-submissions/submissions/serializers.py", line 54, in SubmissionSerializer
    attempt_number = IntegerField(min_value=0)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/rest_framework/fields.py", line 721, in __init__
    message = self.error_messages['min_value'].format(min_value=self.min_value)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/functional.py", line 108, in __wrapper__
    res = func(*self.__args, **self.__kw)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/__init__.py", line 86, in ugettext
    return _trans.ugettext(message)
  File "/edx/app/edxapp/edx-platform/common/djangoapps/monkey_patch/django_utils_translation.py", line 70, in dont_translate_empty_string
    message = function(message)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 278, in ugettext
    return do_translate(message, 'ugettext')
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 268, in do_translate
    _default = translation(settings.LANGUAGE_CODE)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 183, in translation
    default_translation = _fetch(settings.LANGUAGE_CODE)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py", line 160, in _fetch
    app = import_module(appname)
  File "/edx/app/edxapp/venvs/edxapp/local/lib/python2.7/site-packages/django/utils/importlib.py", line 35, in import_module
    __import__(name)
  File "/edx/xblocks/xblock-problem-builder/problem_builder/__init__.py", line 4, in <module>
    from .dashboard import DashboardBlock
  File "/edx/xblocks/xblock-problem-builder/problem_builder/dashboard.py", line 36, in <module>
    from .mcq import MCQBlock
  File "/edx/xblocks/xblock-problem-builder/problem_builder/mcq.py", line 31, in <module>
    from .sub_api import sub_api, SubmittingXBlockMixin
  File "/edx/xblocks/xblock-problem-builder/problem_builder/sub_api.py", line 25, in <module>
    from submissions import api as sub_api
ImportError: cannot import name api

Essentially, two django apps (cms.djangoapps.contentstore and rest_framework) are calling ugettext() at import time (i.e. when the CMS starts up), and as you can see in the trace above, this leads to a circular import of the edx-submissions API.

Fix:
A complete fix would probably involve changing ugettext to ugettext_lazy in any import-time code of all django apps used by the platform, but that is an involved undertaking and can lead to subtle bugs.

So I have worked around the issue by fixing problem-builder so it doesn't load dashboard.py when imported as a django app (which was not necessary). This does change the import path for the XBlock, but I'm not aware of any third party code that would be using that import.

[antoviaque]

It seem like a good approach given the explanations you've put in the description, and a relatively straightforward change. I'm only with a tablet now so I can't test the change - I'll see if someone else from the team can take care of it tomorrow morning. 👍 once this has been tested.

[itsjeyd]

👍

[macdiesel]

I'm good with this approach. The imports in __init__.py were likely to cause issues with the django 1.8 upgrade anyway. 👍