Add JSON encoder for datetimes to xml export

During policy export, we want to write any python datetime objects found
as iso timestamps, rather than throwing exceptions.

common/lib/xmodule/xmodule/modulestore/xml_exporter.py

@@ -3,7 +3,24 @@ from xmodule.modulestore import Location
 from xmodule.modulestore.inheritance import own_metadata
 from fs.osfs import OSFS
 from json import dumps
-
+import json
+from json.encoder import JSONEncoder
+import datetime
+
+class EdxJSONEncoder(json.JSONEncoder):
+    def default(self, obj):
+        if isinstance(obj, Location):
+            return obj.url()
+        elif isinstance(obj, datetime.datetime):
+            if obj.tzinfo is not None:
+                if obj.utcoffset() is None:
+                    return obj.isoformat() + 'Z'
+                else:
+                    return obj.isoformat()
+            else:
+                return obj.isoformat()
+        else:
+            return super(EdxJSONEncoder, self).default(obj)
 
 def export_to_xml(modulestore, contentstore, course_location, root_dir, course_dir, draft_modulestore=None):
 
@@ -35,12 +52,12 @@ def export_to_xml(modulestore, contentstore, course_location, root_dir, course_d
     policies_dir = export_fs.makeopendir('policies')
     course_run_policy_dir = policies_dir.makeopendir(course.location.name)
     with course_run_policy_dir.open('grading_policy.json', 'w') as grading_policy:
-        grading_policy.write(dumps(course.grading_policy))
+        grading_policy.write(dumps(course.grading_policy, cls=EdxJSONEncoder))
 
     # export all of the course metadata in policy.json
     with course_run_policy_dir.open('policy.json', 'w') as course_policy:
         policy = {'course/' + course.location.name: own_metadata(course)}
-        course_policy.write(dumps(policy))
+        course_policy.write(dumps(policy, cls=EdxJSONEncoder))
 
     # export draft content
     # NOTE: this code assumes that verticals are the top most draftable container

common/lib/xmodule/xmodule/tests/test_export.py

 import unittest
+import pytz
 
+from datetime import datetime, timedelta, tzinfo
 from fs.osfs import OSFS
+from mock import Mock
 from path import path
 from tempfile import mkdtemp
 import shutil
 
 from xmodule.modulestore.xml import XMLModuleStore
+from xmodule.modulestore.xml_exporter import EdxJSONEncoder
+
+from xmodule.modulestore import Location
 
 # from ~/mitx_all/mitx/common/lib/xmodule/xmodule/tests/
 # to   ~/mitx_all/mitx/common/test
@@ -127,3 +133,58 @@ class RoundTripTestCase(unittest.TestCase):
 
     def test_word_cloud_roundtrip(self):
         self.check_export_roundtrip(DATA_DIR, "word_cloud")
+
+
+class TestEdxJsonEncoder(unittest.TestCase):
+    def setUp(self):
+        self.encoder = EdxJSONEncoder()
+
+        class OffsetTZ(tzinfo):
+            """A timezone with non-None utcoffset"""
+            def utcoffset(self, dt):
+                return timedelta(hours=4)
+
+        self.offset_tz = OffsetTZ()
+
+        class NullTZ(tzinfo):
+            """A timezone with None as its utcoffset"""
+            def utcoffset(self, dt):
+                return None
+        self.null_utc_tz = NullTZ()
+
+    def test_encode_location(self):
+        loc = Location('i4x', 'org', 'course', 'category', 'name')
+        self.assertEqual(loc.url(), self.encoder.default(loc))
+
+        loc = Location('i4x', 'org', 'course', 'category', 'name', 'version')
+        self.assertEqual(loc.url(), self.encoder.default(loc))
+
+    def test_encode_naive_datetime(self):
+        self.assertEqual(
+            "2013-05-03T10:20:30.000100",
+            self.encoder.default(datetime(2013, 5, 3, 10, 20, 30, 100))
+        )
+        self.assertEqual(
+            "2013-05-03T10:20:30",
+            self.encoder.default(datetime(2013, 5, 3, 10, 20, 30))
+        )
+
+    def test_encode_utc_datetime(self):
+        self.assertEqual(
+            "2013-05-03T10:20:30+00:00",
+            self.encoder.default(datetime(2013, 5, 3, 10, 20, 30, 0, pytz.UTC))
+        )
+
+        self.assertEqual(
+            "2013-05-03T10:20:30+04:00",
+            self.encoder.default(datetime(2013, 5, 3, 10, 20, 30, 0, self.offset_tz))
+        )
+
+        self.assertEqual(
+            "2013-05-03T10:20:30Z",
+            self.encoder.default(datetime(2013, 5, 3, 10, 20, 30, 0, self.null_utc_tz))
+        )
+
+    def test_other_classes(self):
+        with self.assertRaises(TypeError):
+            self.encoder.default(None)

common/lib/xmodule/xmodule/xml_module.py

@@ -10,6 +10,7 @@ from xblock.core import Dict, Scope
 from xmodule.x_module import (XModuleDescriptor, policy_key)
 from xmodule.modulestore import Location
 from xmodule.modulestore.inheritance import own_metadata
+from xmodule.modulestore.xml_exporter import EdxJSONEncoder
 
 log = logging.getLogger(__name__)
 
@@ -84,7 +85,7 @@ def serialize_field(value):
 
         By default, this is the result of calling json.dumps on the input value.
         """
-    return json.dumps(value)
+    return json.dumps(value, cls=EdxJSONEncoder)
 
 
 def deserialize_field(field, value):