bpo-26680: Adds Decimal.is_integer to the Python and C implementations.

The C implementation of Decimal already implements and uses mpd_isinteger internally, we just expose the existing function to Python. The Python implementation uses internal conversion to integer using to_integral_value(). In both cases, the corresponding context methods are also implemented. Tests and documentation are included.
python · mdickinson · Oct 1, 2020 · Mar 13, 2018 · Mar 13, 2018 · Mar 13, 2018
commit 54ca820694afef68f71d1781167efce71e845ab2
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
@@ -621,6 +621,13 @@ Decimal objects
       Return :const:`True` if the argument is either positive or negative
       infinity and :const:`False` otherwise.
 
+   .. method:: is_integer()
+
+      Return :const:`True` if the argument is a finite integral value and
+      :const:`False` otherwise.
+
+      .. versionadded:: 3.10
+
    .. method:: is_nan()
 
       Return :const:`True` if the argument is a (quiet or signaling) NaN and
@@ -1215,6 +1222,13 @@ In addition to the three supplied contexts, new contexts can be created with the
       Returns ``True`` if *x* is infinite; otherwise returns ``False``.
 
 
+   .. method:: is_integer(x)
+
+      Returns ``True`` if *x* is finite and integral; otherwise
+      returns ``False``.
+
+      .. versionadded:: 3.10
+
    .. method:: is_nan(x)
 
       Returns ``True`` if *x* is a qNaN or sNaN; otherwise returns ``False``.

diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
@@ -3164,6 +3164,12 @@ def is_zero(self):
         """Return True if self is a zero; otherwise return False."""
         return not self._is_special and self._int == '0'
 
+    def is_integer(self):
+        """Return True is self is finite and integral; otherwise False."""
+        if self._is_special:
+            return False
+        return self.to_integral_value(rounding=ROUND_FLOOR) == self
+
     def _ln_exp_bound(self):
         """Compute a lower bound for the adjusted exponent of self.ln().
         In other words, compute r such that self.ln() >= 10**r.  Assumes
@@ -4659,6 +4665,25 @@ def is_zero(self, a):
         a = _convert_other(a, raiseit=True)
         return a.is_zero()
 
+    def is_integer(self, a):
+        """Return True if the operand is integral; otherwise return False.
+
+        >>> ExtendedContext.is_integer(Decimal('0'))
+        True
+        >>> ExtendedContext.is_integer(Decimal('2.50'))
+        False
+        >>> ExtendedContext.is_integer(Decimal('-0E+2'))
+        True
+        >>> ExtendedContext.is_integer(Decimal('-0.5'))
+        False
+        >>> ExtendedContext.is_integer(Decimal('NaN'))
+        False
+        >>> ExtendedContext.is_integer(10)
+        True
+        """
+        a = _convert_other(a, raiseit=True)
+        return a.is_integer()
+
     def ln(self, a):
         """Returns the natural (base e) logarithm of the operand.
 

diff --git a/Lib/test/decimaltestdata/extra.decTest b/Lib/test/decimaltestdata/extra.decTest
@@ -2346,6 +2346,24 @@ bool2096 iszero sNaN -> 0
 bool2097 iszero -sNaN -> 0
 bool2098 iszero sNaN123 -> 0
 bool2099 iszero -sNaN123 -> 0
+bool2100 is_integer -1.0 -> 1
+bool2101 is_integer 0.0 -> 1
+bool2102 is_integer 1.0 -> 1
+bool2103 is_integer 42 -> 1
+bool2104 is_integer 1e2 -> 1
+bool2105 is_integer 1.5 -> 0
+bool2106 is_integer 1e-2 -> 0
+bool2107 is_integer NaN -> 0
+bool2109 is_integer -NaN -> 0
+bool2110 is_integer NaN123 -> 0
+bool2111 is_integer -NaN123 -> 0
+bool2112 is_integer sNaN -> 0
+bool2113 is_integer -sNaN -> 0
+bool2114 is_integer sNaN123 -> 0
+bool2115 is_integer -sNaN123 -> 0
+bool2116 is_integer Infinity -> 0
+bool2117 is_integer -Infinity -> 0
+
 
 ------------------------------------------------------------------------
 -- The following tests (pwmx0 through pwmx440) are for the            --

diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
@@ -276,6 +276,7 @@ def setUp(self):
                                  'is_snan',
                                  'is_subnormal',
                                  'is_zero',
+                                 'is_integer',
                                  'same_quantum')
 
     def read_unlimited(self, v, context):
@@ -2726,6 +2727,7 @@ def test_named_parameters(self):
             self.assertRaises(TypeError, D(1).is_snan, context=xc)
             self.assertRaises(TypeError, D(1).is_signed, context=xc)
             self.assertRaises(TypeError, D(1).is_zero, context=xc)
+            self.assertRaises(TypeError, D(1).is_integer, context=xc)
 
             self.assertFalse(D("0.01").is_normal(context=xc))
             self.assertTrue(D("0.01").is_subnormal(context=xc))
@@ -3197,6 +3199,15 @@ def test_is_zero(self):
         self.assertEqual(c.is_zero(10), d)
         self.assertRaises(TypeError, c.is_zero, '10')
 
+    def test_is_integer(self):
+        Decimal = self.decimal.Decimal
+        Context = self.decimal.Context
+
+        c = Context()
+        b = c.is_integer(Decimal(10))
+        self.assertEqual(c.is_integer(10), b)
+        self.assertRaises(TypeError, c.is_integer, '10')
+
     def test_ln(self):
         Decimal = self.decimal.Decimal
         Context = self.decimal.Context
@@ -4360,6 +4371,19 @@ def test_implicit_context(self):
             self.assertTrue(Decimal("-1").is_signed())
             self.assertTrue(Decimal("0").is_zero())
             self.assertTrue(Decimal("0").is_zero())
+            self.assertTrue(Decimal("-1").is_integer())
+            self.assertTrue(Decimal("0").is_integer())
+            self.assertTrue(Decimal("1").is_integer())
+            self.assertTrue(Decimal("42").is_integer())
+            self.assertTrue(Decimal("1e2").is_integer())
+            self.assertFalse(Decimal("1.5").is_integer())
+            self.assertFalse(Decimal("1e-2").is_integer())
+            self.assertFalse(Decimal("NaN").is_integer())
+            self.assertFalse(Decimal("-NaN").is_integer())
+            self.assertFalse(Decimal("sNaN").is_integer())
+            self.assertFalse(Decimal("-sNaN").is_integer())
+            self.assertFalse(Decimal("Inf").is_integer())
+            self.assertFalse(Decimal("-Inf").is_integer())
 
         # Copy
         with localcontext() as c:

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
@@ -4138,6 +4138,7 @@ Dec_BoolFunc(mpd_isqnan)
 Dec_BoolFunc(mpd_issnan)
 Dec_BoolFunc(mpd_issigned)
 Dec_BoolFunc(mpd_iszero)
+Dec_BoolFunc(mpd_isinteger)
 
 /* Boolean functions, optional context arg */
 Dec_BoolFuncVA(mpd_isnormal)
@@ -4772,6 +4773,7 @@ static PyMethodDef dec_methods [] =
   { "is_snan", dec_mpd_issnan, METH_NOARGS, doc_is_snan },
   { "is_signed", dec_mpd_issigned, METH_NOARGS, doc_is_signed },
   { "is_zero", dec_mpd_iszero, METH_NOARGS, doc_is_zero },
+  { "is_integer", dec_mpd_isinteger, METH_NOARGS, doc_is_integer},
 
   /* Boolean functions, optional context arg */
   { "is_normal", (PyCFunction)(void(*)(void))dec_mpd_isnormal, METH_VARARGS|METH_KEYWORDS, doc_is_normal },
@@ -5183,6 +5185,7 @@ DecCtx_BoolFunc_NO_CTX(mpd_isqnan)
 DecCtx_BoolFunc_NO_CTX(mpd_issigned)
 DecCtx_BoolFunc_NO_CTX(mpd_issnan)
 DecCtx_BoolFunc_NO_CTX(mpd_iszero)
+DecCtx_BoolFunc_NO_CTX(mpd_isinteger)
 
 static PyObject *
 ctx_iscanonical(PyObject *context UNUSED, PyObject *v)
@@ -5464,6 +5467,7 @@ static PyMethodDef context_methods [] =
   { "is_snan", ctx_mpd_issnan, METH_O, doc_ctx_is_snan },
   { "is_subnormal", ctx_mpd_issubnormal, METH_O, doc_ctx_is_subnormal },
   { "is_zero", ctx_mpd_iszero, METH_O, doc_ctx_is_zero },
+  { "is_integer", ctx_mpd_isinteger, METH_O, doc_ctx_is_integer },
 
   /* Functions with a single decimal argument */
   { "_apply", PyDecContext_Apply, METH_O, NULL }, /* alias for apply */
@@ -6097,5 +6101,3 @@ PyInit__decimal(void)
 
     return NULL; /* GCOV_NOT_REACHED */
 }
-
-
diff --git a/Modules/_decimal/docstrings.h b/Modules/_decimal/docstrings.h
@@ -260,6 +260,11 @@ Return True if the argument is a (positive or negative) zero and False\n\
 otherwise.\n\
 \n");
 
+PyDoc_STRVAR(doc_is_integer,
+"is_integer($self, /)\n--\n\n\
+Return True if the argument is finite and integral, otherwise False.\n\
+\n");
+
 PyDoc_STRVAR(doc_ln,
 "ln($self, /, context=None)\n--\n\n\
 Return the natural (base e) logarithm of the operand. The function always\n\
@@ -685,6 +690,11 @@ PyDoc_STRVAR(doc_ctx_is_zero,
 Return True if x is a zero, False otherwise.\n\
 \n");
 
+PyDoc_STRVAR(doc_ctx_is_integer,
+"is_integer($self, x, /)\n--\n\n\
++Return True if x is finite and integral, False otherwise.\n\
++\n");
+
 PyDoc_STRVAR(doc_ctx_ln,
 "ln($self, x, /)\n--\n\n\
 Return the natural (base e) logarithm of x.\n\
@@ -879,6 +889,3 @@ Convert a number to a string using scientific notation.\n\
 
 
 #endif /* DOCSTRINGS_H */
-
-
-
diff --git a/Objects/clinic/longobject.c.h b/Objects/clinic/longobject.c.h
diff --git a/Objects/longobject.c b/Objects/longobject.c
@@ -5241,7 +5241,7 @@ Returns True for all integers.
 
 static PyObject *
 int_is_integer_impl(PyObject *self)
-/*[clinic end generated code: output=90f8e794ce5430ef input=903121d57b734c35]*/
+/*[clinic end generated code: output=90f8e794ce5430ef input=1c1a86957301d26d]*/
 {
     Py_RETURN_TRUE;
 }