From 5bb7db2d6f939ba0626eb606102f478a4e613647 Mon Sep 17 00:00:00 2001
From: Keith Bussell <kbussell@gmail.com>
Date: Fri, 3 Aug 2018 12:42:38 -0700
Subject: [PATCH 1/3] Always pass a valid rounding value

Fixes #6015

Prevent an exception in `quantize()` when monkey-patching the decimal
library as cdecimal in Python 2 environments by always passing a valid
(not None) `rounding` value to `quantize()`.
---
 rest_framework/fields.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 3278cf51c..d5071a1aa 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1135,11 +1135,12 @@ class DecimalField(Field):
             return value
 
         context = decimal.getcontext().copy()
+        rounding = context.rounding if self.rounding is None else self.rounding
         if self.max_digits is not None:
             context.prec = self.max_digits
         return value.quantize(
             decimal.Decimal('.1') ** self.decimal_places,
-            rounding=self.rounding,
+            rounding=rounding,
             context=context
         )
 

From 6a42128ddf4a0a053ae95d4db65c67441db3e838 Mon Sep 17 00:00:00 2001
From: Keith Bussell <kbussell@gmail.com>
Date: Mon, 6 Aug 2018 21:39:10 -0700
Subject: [PATCH 2/3] Add Python 2.7-specific comment

---
 rest_framework/fields.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index d5071a1aa..92caa6a38 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1135,6 +1135,7 @@ class DecimalField(Field):
             return value
 
         context = decimal.getcontext().copy()
+        # For Python 2.7 compatibility when using cdecimal
         rounding = context.rounding if self.rounding is None else self.rounding
         if self.max_digits is not None:
             context.prec = self.max_digits

From 602eec8fa0a1e54be6cbd2c5945eb18f5bce5820 Mon Sep 17 00:00:00 2001
From: Keith Bussell <kbussell@gmail.com>
Date: Mon, 6 Aug 2018 21:39:46 -0700
Subject: [PATCH 3/3] Add test for monkey-patched decimal in Python 2.7

For #6105
---
 tests/test_fields.py | 16 ++++++++++++++++
 tox.ini              |  1 +
 2 files changed, 17 insertions(+)

diff --git a/tests/test_fields.py b/tests/test_fields.py
index aa3391a72..27d947cd0 100644
--- a/tests/test_fields.py
+++ b/tests/test_fields.py
@@ -7,6 +7,7 @@ from decimal import ROUND_DOWN, ROUND_UP, Decimal
 
 import pytest
 import pytz
+from _pytest.monkeypatch import MonkeyPatch
 from django.core.exceptions import ValidationError as DjangoValidationError
 from django.http import QueryDict
 from django.test import TestCase, override_settings
@@ -17,6 +18,11 @@ import rest_framework
 from rest_framework import exceptions, serializers
 from rest_framework.fields import DjangoImageField, is_simple_callable
 
+try:
+    import cdecimal
+except ImportError:
+    cdecimal = False
+
 try:
     import typings
 except ImportError:
@@ -1128,6 +1134,16 @@ class TestQuantizedValueForDecimal(TestCase):
         expected_digit_tuple = (0, (1, 2, 0, 0), -2)
         assert value == expected_digit_tuple
 
+    @unittest.skipUnless(cdecimal, 'requires python 2.7')
+    def test_quantize_on_monkey_patched_cdecimal(self):
+        # Monkey-patch cdecimal to replace decimal in for DecimalField
+        monkeypatch = MonkeyPatch()
+
+        with monkeypatch.context() as m:
+            m.setattr('rest_framework.fields.decimal', cdecimal)
+            f = rest_framework.fields.DecimalField(max_digits=4, decimal_places=2)
+            f.quantize(cdecimal.Decimal('1.234'))
+
 
 class TestNoDecimalPlaces(FieldValues):
     valid_inputs = {
diff --git a/tox.ini b/tox.ini
index 11c37ccfc..0a4e34020 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,6 +24,7 @@ deps =
         django20: Django>=2.0,<2.1
         django21: Django>=2.1b1,<2.2
         djangomaster: https://github.com/django/django/archive/master.tar.gz
+        py27: m3-cdecimal
         -rrequirements/requirements-testing.txt
         -rrequirements/requirements-optionals.txt