Remove request.POST save - incompatible with DRF v3.6.3.

[doctoryes]

DRF v3.6.3 doesn't allow request.POST to be changed for DRF Requests. This change makes the Python unittests pass again.

@bdero Was there a reason for this statement? The request isn't accessed further in this method.

[doctoryes]

As you can see by the code below, modifying request.POST for a rest_framework.request.Request is non-standard and requires a workaround:
https://github.com/edx/edx-platform/blob/master/openedx/core/djangoapps/user_api/helpers.py#L411-L417
We should avoid doing so if possible.

[doctoryes]

The request.POST attribute changed to a @property between releases 3.2.4 and 3.3.1 - here's the PR: encode/django-rest-framework#3592

[brittneyexline]

i see that self.request gets passed in to students_update_enrollment below, and that function accesses request.POST. however, i don't understand if self.request and request are the same object?

[doctoryes]

It appears they are:

ipdb> id(request)
140610886734992
ipdb> id(self.request)
140610886734992

but it also appears that request.POST is the same as request.data:

ipdb> p request.POST
<QueryDict: {u'action': [u'enroll'], u'courses': [u'org.1/course_1/Run_1'], u'identifiers': [u'robot+test+5@edx.org'], u'email_students': [u'False']}>
ipdb> p request.data
<QueryDict: {u'action': [u'enroll'], u'courses': [u'org.1/course_1/Run_1'], u'identifiers': [u'robot+test+5@edx.org'], u'email_students': [u'False']}>
ipdb> id(request.POST)
140610886285712
ipdb> id(request.data)
140610886285712

So I'm unsure if there's a reason why this line exists.

[bdero]

@doctoryes I'm currently verifying this change

[brittneyexline]

thanks for the clarification on that @doctoryes. approving this, if something comes up from @bdero's verification, i suggest addressing those issues in https://github.com/edx/edx-platform/pull/15579.

[macdiesel]

It's unclear to me why this was even done in the first place.

[bdero]

@doctoryes @brittneyexline I've tested this carefully, although it's difficult to test some aspects completely with this bug still present. 👍 I don't see a reason why this should be necessary as well.

@macdiesel This feature was initially built by another dev group and I didn't notice this line during the initial rebasing. It's possible that this was needed for a prior DRF version as the blame says it was introduced in a commit that fixes the feature for a version range of DRF.

[doctoryes]

Thanks for the prompt review, @bdero .

[edx-pipeline-bot]

EdX Release Notice: This PR has been deployed to the staging environment in preparation for a release to production on Tuesday, July 18, 2017.

[edx-pipeline-bot]

EdX Release Notice: This PR has been deployed to the production environment.