Add test_pow from CPython 3.8

Author: palaviv

Lib/test/test_pow.py

@@ -0,0 +1,123 @@
+import unittest
+
+class PowTest(unittest.TestCase):
+
+    def powtest(self, type):
+        if type != float:
+            for i in range(-1000, 1000):
+                self.assertEqual(pow(type(i), 0), 1)
+                self.assertEqual(pow(type(i), 1), type(i))
+                self.assertEqual(pow(type(0), 1), type(0))
+                self.assertEqual(pow(type(1), 1), type(1))
+
+            for i in range(-100, 100):
+                self.assertEqual(pow(type(i), 3), i*i*i)
+
+            pow2 = 1
+            for i in range(0, 31):
+                self.assertEqual(pow(2, i), pow2)
+                if i != 30 : pow2 = pow2*2
+
+            for othertype in (int,):
+                for i in list(range(-10, 0)) + list(range(1, 10)):
+                    ii = type(i)
+                    for j in range(1, 11):
+                        jj = -othertype(j)
+                        pow(ii, jj)
+
+        for othertype in int, float:
+            for i in range(1, 100):
+                zero = type(0)
+                exp = -othertype(i/10.0)
+                if exp == 0:
+                    continue
+                self.assertRaises(ZeroDivisionError, pow, zero, exp)
+
+        il, ih = -20, 20
+        jl, jh = -5,   5
+        kl, kh = -10, 10
+        asseq = self.assertEqual
+        if type == float:
+            il = 1
+            asseq = self.assertAlmostEqual
+        elif type == int:
+            jl = 0
+        elif type == int:
+            jl, jh = 0, 15
+        for i in range(il, ih+1):
+            for j in range(jl, jh+1):
+                for k in range(kl, kh+1):
+                    if k != 0:
+                        if type == float or j < 0:
+                            self.assertRaises(TypeError, pow, type(i), j, k)
+                            continue
+                        asseq(
+                            pow(type(i),j,k),
+                            pow(type(i),j)% type(k)
+                        )
+
+    def test_powint(self):
+        self.powtest(int)
+
+    def test_powfloat(self):
+        self.powtest(float)
+
+    def test_other(self):
+        # Other tests-- not very systematic
+        self.assertEqual(pow(3,3) % 8, pow(3,3,8))
+        self.assertEqual(pow(3,3) % -8, pow(3,3,-8))
+        self.assertEqual(pow(3,2) % -2, pow(3,2,-2))
+        self.assertEqual(pow(-3,3) % 8, pow(-3,3,8))
+        self.assertEqual(pow(-3,3) % -8, pow(-3,3,-8))
+        self.assertEqual(pow(5,2) % -8, pow(5,2,-8))
+
+        self.assertEqual(pow(3,3) % 8, pow(3,3,8))
+        self.assertEqual(pow(3,3) % -8, pow(3,3,-8))
+        self.assertEqual(pow(3,2) % -2, pow(3,2,-2))
+        self.assertEqual(pow(-3,3) % 8, pow(-3,3,8))
+        self.assertEqual(pow(-3,3) % -8, pow(-3,3,-8))
+        self.assertEqual(pow(5,2) % -8, pow(5,2,-8))
+
+        for i in range(-10, 11):
+            for j in range(0, 6):
+                for k in range(-7, 11):
+                    if j >= 0 and k != 0:
+                        self.assertEqual(
+                            pow(i,j) % k,
+                            pow(i,j,k)
+                        )
+                    if j >= 0 and k != 0:
+                        self.assertEqual(
+                            pow(int(i),j) % k,
+                            pow(int(i),j,k)
+                        )
+
+    def test_bug643260(self):
+        class TestRpow:
+            def __rpow__(self, other):
+                return None
+        None ** TestRpow() # Won't fail when __rpow__ invoked.  SF bug #643260.
+
+    def test_bug705231(self):
+        # -1.0 raised to an integer should never blow up.  It did if the
+        # platform pow() was buggy, and Python didn't worm around it.
+        eq = self.assertEqual
+        a = -1.0
+        # The next two tests can still fail if the platform floor()
+        # function doesn't treat all large inputs as integers
+        # test_math should also fail if that is happening
+        eq(pow(a, 1.23e167), 1.0)
+        eq(pow(a, -1.23e167), 1.0)
+        for b in range(-10, 11):
+            eq(pow(a, float(b)), b & 1 and -1.0 or 1.0)
+        for n in range(0, 100):
+            fiveto = float(5 ** n)
+            # For small n, fiveto will be odd.  Eventually we run out of
+            # mantissa bits, though, and thereafer fiveto will be even.
+            expected = fiveto % 2.0 and -1.0 or 1.0
+            eq(pow(a, fiveto), expected)
+            eq(pow(a, -fiveto), expected)
+        eq(expected, 1.0)   # else we didn't push fiveto to evenness
+
+if __name__ == "__main__":
+    unittest.main()