Address upstream review comments.

requirements.txt

-django>=1.4, <1.5
 pyyaml
 -e git+https://github.com/edx/XBlock.git@tag-master-2015-05-22#egg=XBlock
 -e git+https://github.com/edx/xblock-utils.git@b4f9b51146c7fafa12f41d54af752b8f1516dffd#egg=xblock-utils

test-requirements.txt

+django>=1.4, <1.5
 -r requirements.txt
 -e git+https://github.com/edx/xblock-sdk.git@629650ed6fc1b77d1a5287debeace0b29db7c0fd#egg=xblock-sdk
 ddt

vectordraw/grader.py

 """
 This module contains grading logic for Vector Drawing exercises.
+
+It uses the following data structures:
+
+- `vectors`: A dictionary of Vector objects.
+
+   Keys are vector names and values represent individual vectors that were present
+   on the drawing board when the student submitted an answer by clicking the 'Check' button.
+
+- `points`: A dictionary of Point objects.
+
+   Keys are point names and values represent individual points that were present
+   on the drawing board when the student submitted an answer by clicking the 'Check' button.
+
+- `check`: A dictionary representing a specific check.
+
+   Contains the name of the check itself (e.g., 'presence', 'coords', 'angle'),
+   the name of the element on which to perform the check, as well as
+   the expected value of the property being checked.
+   Optionally contains information about tolerance to apply when performing the check,
+   and/or a custom error message to present to the user if the check fails.
+
+- `answer`: A dictionary representing a specific answer submitted by a student.
+
+   Contains three entries: vectors, points, and checks. The first two (vectors, points)
+   provide information about vectors and points present on the drawing board
+   when the answer was submitted. The third one (checks) specifies the checks
+   to perform for individual vectors and points.
+
 """
 
 # pylint: disable=invalid-name
@@ -52,28 +80,36 @@ def check_presence(check, vectors):
         return errmsg.format(name=check['vector'])
 
 
-def check_tail(check, vectors):
+def _check_vector_endpoint(check, vectors, endpoint):
     """
-    Check if tail of vector targeted by `check` is in correct position.
+    Check if `endpoint` (tail or tip) of vector targeted by `check` is in correct position.
     """
     vec = vectors[check['vector']]
     tolerance = check.get('tolerance', 1.0)
     expected = check['expected']
-    dist = math.hypot(expected[0] - vec.tail.x, expected[1] - vec.tail.y)
+    verb = 'start' if endpoint == 'tail' else 'end'
+    endpoint = getattr(vec, endpoint)
+    dist = math.hypot(expected[0] - endpoint.x, expected[1] - endpoint.y)
     if dist > tolerance:
-        return _errmsg('Vector {name} does not start at correct point.', check, vectors)
+        return _errmsg(
+            'Vector {name} does not {verb} at correct point.'.format(name='{name}', verb=verb),
+            check,
+            vectors
+        )
+
+
+def check_tail(check, vectors):
+    """
+    Check if tail of vector targeted by `check` is in correct position.
+    """
+    return _check_vector_endpoint(check, vectors, endpoint='tail')
 
 
 def check_tip(check, vectors):
     """
     Check if tip of vector targeted by `check` is in correct position.
     """
-    vec = vectors[check['vector']]
-    tolerance = check.get('tolerance', 1.0)
-    expected = check['expected']
-    dist = math.hypot(expected[0] - vec.tip.x, expected[1] - vec.tip.y)
-    if dist > tolerance:
-        return _errmsg('Vector {name} does not end at correct point.', check, vectors)
+    return _check_vector_endpoint(check, vectors, endpoint='tip')
 
 
 def _check_coordinate(check, coord):
@@ -235,7 +271,7 @@ def check_points_on_line(check, vectors):
     """
     line = vectors[check['vector']]
     tolerance = check.get('tolerance', 1.0)
-    points = check.get('expected')
+    points = check['expected']
     for point in points:
         point = Point(point[0], point[1])
         if _dist_line_point(line, point) > tolerance:
@@ -250,7 +286,7 @@ def check_point_coords(check, points):
     """
     point = points[check['point']]
     tolerance = check.get('tolerance', 1.0)
-    expected = check.get('expected')
+    expected = check['expected']
     dist = math.hypot(expected[0] - point.x, expected[1] - point.y)
     if dist > tolerance:
         return _errmsg_point('Point {name} is not at the correct location.', check, point)

vectordraw/templates/html/vectordraw_edit.html

@@ -43,7 +43,7 @@
                         aria-describedby="{{field.name}}-help"
                         rows=10 cols=70>{{field.value}}</textarea>
             {% else %}
-              Unsupported field type. This setting cannot be edited.
+              {% trans "Unsupported field type. This setting cannot be edited." %}
             {% endif %}
 
             {% if field.allow_reset %}
@@ -57,7 +57,7 @@
             {% endif %}
           </div>
           {% if field.help %}
-            <span id="{{field.name}}-help" class="tip setting-help"> {{ field.help }} </span>
+            <span id="{{field.name}}-help" class="tip setting-help"> {{ field.help|safe }} </span>
           {% endif %}
         </li>
       {% endfor %}

vectordraw/utils.py

+"""
+This module contains utility functions for the Vector Drawing XBlock.
+"""
+
+
+def get_doc_link(section, link_text="here"):
+    """
+    Return link to specific `section` of README for Vector Drawing exercises.
+    """
+    return (
+        '<a href="https://github.com/open-craft/jsinput-vectordraw#{section}" target="_blank">'
+        '{link_text}'
+        '</a>'
+    ).format(section=section, link_text=link_text)

vectordraw/vectordraw.py

@@ -18,6 +18,7 @@ except ImportError:
     WorkbenchRuntime = False  # pylint: disable=invalid-name
 
 from .grader import Grader
+from .utils import get_doc_link
 
 
 loader = ResourceLoader(__name__)  # pylint: disable=invalid-name
@@ -151,10 +152,11 @@ class VectorDrawXBlock(StudioEditableXBlockMixin, XBlock):
             "List of vectors to use for the exercise. "
             "You must specify it as an array of entries "
             "where each entry represents an individual vector. "
+            "See {doc_link} for more information. "
             "Note that you can also use the WYSIWYG editor below to create or modify vectors. "
             "If you do, any changes you make here will be overwritten by vector data "
             "from the WYSIWYG editor when saving."
-        ),
+        ).format(doc_link=get_doc_link('vectors')),
         default="[]",
         multiline_editor=True,
         resettable_editor=False,
@@ -166,8 +168,9 @@ class VectorDrawXBlock(StudioEditableXBlockMixin, XBlock):
         help=(
             "List of points to be drawn on the board for reference, or to be placed by the student."
             "You must specify it as an array of entries "
-            "where each entry represents an individual point."
-        ),
+            "where each entry represents an individual point. "
+            "See {doc_link} for more information."
+        ).format(doc_link=get_doc_link('points')),
         default="[]",
         multiline_editor=True,
         resettable_editor=False,
@@ -178,12 +181,16 @@ class VectorDrawXBlock(StudioEditableXBlockMixin, XBlock):
         display_name="Expected result",
         help=(
             "Defines vector properties for grading. "
+            "You must specify it as a JSON object where each key is the name of an existing vector "
+            "and each value is a JSON object containing information about checks to perform "
+            "and expected values. "
+            "See {doc_link} for more information. "
             "Vectors omitted from this setting are ignored when grading. "
             "Note that you can also use the WYSIWYG editor below to opt in and out of checks "
             "for individual vectors. "
             "If you use the WYSIWYG editor at all, any changes you make here "
             "will be overwritten when saving."
-        ),
+        ).format(doc_link=get_doc_link('expected_result')),
         default="{}",
         multiline_editor=True,
         resettable_editor=False,
@@ -328,9 +335,7 @@ class VectorDrawXBlock(StudioEditableXBlockMixin, XBlock):
         for vector in json.loads(self.vectors):
             default_vector = self._get_default_vector()
             default_vector_style = default_vector['style']
-            if 'style' in vector:
-                default_vector_style.update(vector['style'])
-                del vector['style']
+            default_vector_style.update(vector.pop('style', {}))
             default_vector.update(vector)
             vectors.append(default_vector)
         return vectors
@@ -362,9 +367,7 @@ class VectorDrawXBlock(StudioEditableXBlockMixin, XBlock):
         for point in json.loads(self.points):
             default_point = self._get_default_point()
             default_point_style = default_point['style']
-            if 'style' in point:
-                default_point_style.update(point['style'])
-                del point['style']
+            default_point_style.update(point.pop('style', {}))
             default_point.update(point)
             default_point_style['name'] = default_point['name']
             default_point_style['fixed'] = default_point['fixed']