Fix timezone handling for DateTimeField

requirements/requirements-optionals.txt

@@ -1,4 +1,5 @@
 # Optional packages which may be used with REST framework.
+pytz==2017.2
 markdown==2.6.4
 django-guardian==1.4.8
 django-filter==1.0.4

rest_framework/fields.py

@@ -1125,7 +1125,9 @@ def enforce_timezone(self, value):
         """
         field_timezone = getattr(self, 'timezone', self.default_timezone())
 
-        if (field_timezone is not None) and not timezone.is_aware(value):
+        if field_timezone is not None:
+            if timezone.is_aware(value):
+                return value.astimezone(field_timezone)
             try:
                 return timezone.make_aware(value, field_timezone)
             except InvalidTimeError:
@@ -1135,7 +1137,7 @@ def enforce_timezone(self, value):
         return value
 
     def default_timezone(self):
-        return timezone.get_default_timezone() if settings.USE_TZ else None
+        return timezone.get_current_timezone() if settings.USE_TZ else None
 
     def to_internal_value(self, value):
         input_formats = getattr(self, 'input_formats', api_settings.DATETIME_INPUT_FORMATS)
@@ -1174,6 +1176,7 @@ def to_representation(self, value):
             return value
 
         if output_format.lower() == ISO_8601:
+            value = self.enforce_timezone(value)
             value = value.isoformat()
             if value.endswith('+00:00'):
                 value = value[:-6] + 'Z'

tests/test_fields.py

@@ -10,12 +10,17 @@
 from django.http import QueryDict
 from django.test import TestCase, override_settings
 from django.utils import six
-from django.utils.timezone import utc
+from django.utils.timezone import activate, deactivate, utc
 
 import rest_framework
 from rest_framework import compat, serializers
 from rest_framework.fields import is_simple_callable
 
+try:
+    import pytz
+except ImportError:
+    pytz = None
+
 try:
     import typings
 except ImportError:
@@ -1165,7 +1170,7 @@ class TestDateTimeField(FieldValues):
         datetime.date(2001, 1, 1): ['Expected a datetime but got a date.'],
     }
     outputs = {
-        datetime.datetime(2001, 1, 1, 13, 00): '2001-01-01T13:00:00',
+        datetime.datetime(2001, 1, 1, 13, 00): '2001-01-01T13:00:00Z',
         datetime.datetime(2001, 1, 1, 13, 00, tzinfo=utc): '2001-01-01T13:00:00Z',
         '2001-01-01T00:00:00': '2001-01-01T00:00:00',
         six.text_type('2016-01-10T00:00:00'): '2016-01-10T00:00:00',
@@ -1227,10 +1232,59 @@ class TestNaiveDateTimeField(FieldValues):
         '2001-01-01 13:00': datetime.datetime(2001, 1, 1, 13, 00),
     }
     invalid_inputs = {}
-    outputs = {}
+    outputs = {
+        datetime.datetime(2001, 1, 1, 13, 00): '2001-01-01T13:00:00',
+        datetime.datetime(2001, 1, 1, 13, 00, tzinfo=utc): '2001-01-01T13:00:00',
+    }
     field = serializers.DateTimeField(default_timezone=None)
 
 
+@pytest.mark.skipif(pytz is None, reason='pytz not installed')
+class TestTZWithDateTimeField(FieldValues):
+    """
+    Valid and invalid values for `DateTimeField` when not using UTC as the timezone.
+    """
+    @classmethod
+    def setup_class(cls):
+        # use class setup method, as class-level attribute will still be evaluated even if test is skipped
+        kolkata = pytz.timezone('Asia/Kolkata')
+
+        cls.valid_inputs = {
+            '2016-12-19T10:00:00': kolkata.localize(datetime.datetime(2016, 12, 19, 10)),
+            '2016-12-19T10:00:00+05:30': kolkata.localize(datetime.datetime(2016, 12, 19, 10)),
+            datetime.datetime(2016, 12, 19, 10): kolkata.localize(datetime.datetime(2016, 12, 19, 10)),
+        }
+        cls.invalid_inputs = {}
+        cls.outputs = {
+            datetime.datetime(2016, 12, 19, 10): '2016-12-19T10:00:00+05:30',
+            datetime.datetime(2016, 12, 19, 4, 30, tzinfo=utc): '2016-12-19T10:00:00+05:30',
+        }
+        cls.field = serializers.DateTimeField(default_timezone=kolkata)
+
+
+@pytest.mark.skipif(pytz is None, reason='pytz not installed')
+@override_settings(TIME_ZONE='UTC', USE_TZ=True)
+class TestDefaultTZDateTimeField(TestCase):
+    """
+    Test the current/default timezone handling in `DateTimeField`.
+    """
+
+    @classmethod
+    def setup_class(cls):
+        cls.field = serializers.DateTimeField()
+        cls.kolkata = pytz.timezone('Asia/Kolkata')
+
+    def test_default_timezone(self):
+        assert self.field.default_timezone() == utc
+
+    def test_current_timezone(self):
+        assert self.field.default_timezone() == utc
+        activate(self.kolkata)
+        assert self.field.default_timezone() == self.kolkata
+        deactivate()
+        assert self.field.default_timezone() == utc
+
+
 class TestNaiveDayLightSavingTimeTimeZoneDateTimeField(FieldValues):
     """
     Invalid values for `DateTimeField` with datetime in DST shift (non-existing or ambiguous) and timezone with DST.