Fix date summary blocks for courses without an end date.

I also took this opportunity to do some small cleanups of the date
summary code, specifically converting some attributes to properties in
order to remove a Pylint directive disabling warnings about missing
docstrings.

lms/djangoapps/courseware/courses.py

+"""
+Functions for accessing and displaying courses within the
+courseware.
+"""
+from datetime import datetime
 from collections import defaultdict
 from fs.errors import ResourceNotFoundError
 import logging
 import inspect
 
 from path import Path as path
+import pytz
 from django.http import Http404
 from django.conf import settings
 
@@ -334,7 +340,16 @@ def _get_course_date_summary_blocks(course, user):
     )
 
     blocks = (cls(course, user) for cls in block_classes)
-    return sorted((b for b in blocks if b.is_enabled), key=lambda b: b.date)
+
+    def block_key_fn(block):
+        """
+        If the block's date is None, return the maximum datetime in order
+        to force it to the end of the list of displayed blocks.
+        """
+        if block.date is None:
+            return datetime.max.replace(tzinfo=pytz.UTC)
+        return block.date
+    return sorted((b for b in blocks if b.is_enabled), key=block_key_fn)
 
 
 # TODO: Fix this such that these are pulled in as extra course-specific tabs.

lms/djangoapps/courseware/date_summary.py

-# pylint: disable=missing-docstring
 """
 This module provides date summary blocks for the Course Info
 page. Each block gives information about a particular
@@ -20,27 +19,46 @@ from student.models import CourseEnrollment
 class DateSummary(object):
     """Base class for all date summary blocks."""
 
-    # The CSS class of this summary. Indicates the type of information
-    # this summary block contains, and its urgency.
-    css_class = ''
+    @property
+    def css_class(self):
+        """
+        The CSS class of this summary. Indicates the type of information
+        this summary block contains, and its urgency.
+        """
+        return ''
 
-    # The title of this summary.
-    title = ''
+    @property
+    def title(self):
+        """The title of this summary."""
+        return ''
 
-    # The detail text displayed by this summary.
-    description = ''
+    @property
+    def description(self):
+        """The detail text displayed by this summary."""
+        return ''
 
-    # This summary's date.
-    date = None
+    @property
+    def date(self):
+        """This summary's date."""
+        return None
 
-    # The format to display this date in. By default, displays like Jan 01, 2015.
-    date_format = '%b %d, %Y'
+    @property
+    def date_format(self):
+        """
+        The format to display this date in. By default, displays like Jan
+        01, 2015.
+        """
+        return '%b %d, %Y'
 
-    # The location to link to for more information.
-    link = ''
+    @property
+    def link(self):
+        """The location to link to for more information."""
+        return ''
 
-    # The text of the link.
-    link_text = ''
+    @property
+    def link_text(self):
+        """The text of the link."""
+        return ''
 
     def __init__(self, course, user):
         self.course = course
@@ -126,7 +144,10 @@ class CourseEndDate(DateSummary):
     """
     css_class = 'end-date'
     title = _('Course End')
-    is_enabled = True
+
+    @property
+    def is_enabled(self):
+        return self.date is not None
 
     @property
     def description(self):

lms/djangoapps/courseware/tests/test_date_summary.py

@@ -48,11 +48,15 @@ class CourseDateSummaryTest(SharedModuleStoreTestCase):
         """Set up the course and user for this test."""
         now = datetime.now(pytz.UTC)
         self.course = CourseFactory.create(  # pylint: disable=attribute-defined-outside-init
-            start=now + timedelta(days=days_till_start),
-            end=now + timedelta(days=days_till_end),
+            start=now + timedelta(days=days_till_start)
         )
         self.user = UserFactory.create()  # pylint: disable=attribute-defined-outside-init
 
+        if days_till_end is not None:
+            self.course.end = now + timedelta(days=days_till_end)
+        else:
+            self.course.end = None
+
         if enrollment_mode is not None and days_till_upgrade_deadline is not None:
             CourseModeFactory.create(
                 course_id=self.course.id,
@@ -97,6 +101,9 @@ class CourseDateSummaryTest(SharedModuleStoreTestCase):
           'days_till_verification_deadline': -5,
           'verification_status': 'approved'},
          (TodaysDate, CourseEndDate)),
+        # No course end date
+        ({'days_till_end': None},
+         (CourseStartDate, TodaysDate, VerificationDeadlineDate, VerifiedUpgradeDeadlineDate)),
         # During course run
         ({'days_till_start': -1},
          (TodaysDate, CourseEndDate, VerificationDeadlineDate, VerifiedUpgradeDeadlineDate)),
@@ -131,13 +138,6 @@ class CourseDateSummaryTest(SharedModuleStoreTestCase):
         self.assertHTMLEqual(block.render(), html)
         self.assertFalse(block.is_enabled)
 
-    @freezegun.freeze_time('2015-01-02')
-    def test_date_render(self):
-        self.setup_course_and_user()
-        block = DateSummary(self.course, self.user)
-        block.date = datetime.now(pytz.UTC)
-        self.assertIn('Jan 02, 2015', block.render())
-
     ## TodaysDate
 
     @freezegun.freeze_time('2015-01-02')
@@ -149,6 +149,12 @@ class CourseDateSummaryTest(SharedModuleStoreTestCase):
         self.assertEqual(block.title, 'Today is Jan 02, 2015')
         self.assertNotIn('date-summary-date', block.render())
 
+    @freezegun.freeze_time('2015-01-02')
+    def test_date_render(self):
+        self.setup_course_and_user()
+        block = TodaysDate(self.course, self.user)
+        self.assertIn('Jan 02, 2015', block.render())
+
     ## CourseStartDate
 
     def test_course_start_date(self):