Raise InvalidOperation if exponents of zeros are clamped during exact

conversion in the Decimal constructor. Exact here refers to the
representation and not to the value (clamping does not change the value).

Lib/test/test_decimal.py

@@ -4953,6 +4953,30 @@ class CWhitebox(unittest.TestCase):
         self.assertRaises(ValueError, get_fmt, 12345, invalid_dot, 'g')
         self.assertRaises(ValueError, get_fmt, 12345, invalid_sep, 'g')
 
+    def test_exact_conversion(self):
+        Decimal = C.Decimal
+        localcontext = C.localcontext
+        InvalidOperation = C.InvalidOperation
+
+        with localcontext() as c:
+
+            c.traps[InvalidOperation] = True
+
+            # Clamped
+            x = "0e%d" % sys.maxsize
+            self.assertRaises(InvalidOperation, Decimal, x)
+
+            x = "0e%d" % (-sys.maxsize-1)
+            self.assertRaises(InvalidOperation, Decimal, x)
+
+            # Overflow
+            x = "1e%d" % sys.maxsize
+            self.assertRaises(InvalidOperation, Decimal, x)
+
+            # Underflow
+            x = "1e%d" % (-sys.maxsize-1)
+            self.assertRaises(InvalidOperation, Decimal, x)
+
 
 all_tests = [
   CExplicitConstructionTest, PyExplicitConstructionTest,

Modules/_decimal/_decimal.c

@@ -1935,7 +1935,7 @@ PyDecType_FromCStringExact(PyTypeObject *type, const char *s,
     mpd_maxcontext(&maxctx);
 
     mpd_qset_string(MPD(dec), s, &maxctx, &status);
-    if (status & (MPD_Inexact|MPD_Rounded)) {
+    if (status & (MPD_Inexact|MPD_Rounded|MPD_Clamped)) {
         /* we want exact results */
         mpd_seterror(MPD(dec), MPD_Invalid_operation, &status);
     }
@@ -2139,7 +2139,7 @@ PyDecType_FromLongExact(PyTypeObject *type, const PyObject *pylong,
         return NULL;
     }
 
-    if (status & (MPD_Inexact|MPD_Rounded)) {
+    if (status & (MPD_Inexact|MPD_Rounded|MPD_Clamped)) {
         /* we want exact results */
         mpd_seterror(MPD(dec), MPD_Invalid_operation, &status);
     }

Modules/_decimal/tests/deccheck.py

@@ -302,6 +302,7 @@ def RestrictedDecimal(value):
     dec = maxcontext.create_decimal(value)
     if maxcontext.flags[P.Inexact] or \
        maxcontext.flags[P.Rounded] or \
+       maxcontext.flags[P.Clamped] or \
        maxcontext.flags[P.InvalidOperation]:
         return context.p._raise_error(P.InvalidOperation)
     if maxcontext.flags[P.FloatOperation]: