[3.12] gh-118164: str(10**10000) hangs if the C _decimal module is missing (GH-118503) (GH-118584)

Serhiy and I independently concluded that exact powers of 10
aren't possible in these contexts, so just checking the
string length is sufficient.

(cherry picked from commit 999f0c512281995fb61a0d9eda075fd846e8c505)

Co-authored-by: Tim Peters <tim.peters@gmail.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 24 insertions, 1 deletions

diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index ea74f6c..1feaf2e 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -4722,9 +4722,33 @@ class PyWhitebox(unittest.TestCase):
 
             c.prec = 1
             x = Decimal("152587890625") ** Decimal('-0.5')
+            self.assertEqual(x, Decimal('3e-6'))
+            c.prec = 2
+            x = Decimal("152587890625") ** Decimal('-0.5')
+            self.assertEqual(x, Decimal('2.6e-6'))
+            c.prec = 3
+            x = Decimal("152587890625") ** Decimal('-0.5')
+            self.assertEqual(x, Decimal('2.56e-6'))
+            c.prec = 28
+            x = Decimal("152587890625") ** Decimal('-0.5')
+            self.assertEqual(x, Decimal('2.56e-6'))
+
             c.prec = 201
             x = Decimal(2**578) ** Decimal("-0.5")
 
+            # See https://github.com/python/cpython/issues/118027
+            # Testing for an exact power could appear to hang, in the Python
+            # version, as it attempted to compute 10**(MAX_EMAX + 1).
+            # Fixed via https://github.com/python/cpython/pull/118503.
+            c.prec = P.MAX_PREC
+            c.Emax = P.MAX_EMAX
+            c.Emin = P.MIN_EMIN
+            c.traps[P.Inexact] = 1
+            D2 = Decimal(2)
+            # If the bug is still present, the next statement won't complete.
+            res = D2 ** 117
+            self.assertEqual(res, 1 << 117)
+
     def test_py_immutability_operations(self):
         # Do operations and check that it didn't change internal objects.
         Decimal = P.Decimal
@@ -5737,7 +5761,6 @@ class CWhitebox(unittest.TestCase):
         with C.localcontext(rounding=C.ROUND_DOWN):
             self.assertEqual(format(y, '#.1f'), '6.0')
 
-
 @requires_docstrings
 @requires_cdecimal
 class SignatureTest(unittest.TestCase):