Refs #28643 -- Added math database functions.

Thanks Nick Pope for much review.

tests/db_functions/math/test_power.py

@@ -0,0 +1,35 @@
+from decimal import Decimal
+
+from django.db.models.functions import Power
+from django.test import TestCase
+
+from ..models import DecimalModel, FloatModel, IntegerModel
+
+
+class PowerTests(TestCase):
+
+    def test_decimal(self):
+        DecimalModel.objects.create(n1=Decimal('1.0'), n2=Decimal('-0.6'))
+        obj = DecimalModel.objects.annotate(n_power=Power('n1', 'n2')).first()
+        self.assertIsInstance(obj.n_power, Decimal)
+        self.assertAlmostEqual(obj.n_power, Decimal(obj.n1 ** obj.n2))
+
+    def test_float(self):
+        FloatModel.objects.create(f1=2.3, f2=1.1)
+        obj = FloatModel.objects.annotate(f_power=Power('f1', 'f2')).first()
+        self.assertIsInstance(obj.f_power, float)
+        self.assertAlmostEqual(obj.f_power, obj.f1 ** obj.f2)
+
+    def test_integer(self):
+        IntegerModel.objects.create(small=-1, normal=20, big=3)
+        obj = IntegerModel.objects.annotate(
+            small_power=Power('small', 'normal'),
+            normal_power=Power('normal', 'big'),
+            big_power=Power('big', 'small'),
+        ).first()
+        self.assertIsInstance(obj.small_power, float)
+        self.assertIsInstance(obj.normal_power, float)
+        self.assertIsInstance(obj.big_power, float)
+        self.assertAlmostEqual(obj.small_power, obj.small ** obj.normal)
+        self.assertAlmostEqual(obj.normal_power, obj.normal ** obj.big)
+        self.assertAlmostEqual(obj.big_power, obj.big ** obj.small)