ENH: Add integer.is_integer

Match `int.is_integer`, which was added in python/cpython#6121

Author: Bas van Beek

numpy/__init__.pyi

@@ -3190,6 +3190,7 @@ class integer(number[_NBit1]):  # type: ignore
         __args: Union[L[0], Tuple[()], Tuple[L[0]]] = ...,
     ) -> int: ...
     def tolist(self) -> int: ...
+    def is_integer(self) -> L[True]: ...
     def __index__(self) -> int: ...
     __truediv__: _IntTrueDiv[_NBit1]
     __rtruediv__: _IntTrueDiv[_NBit1]

numpy/core/_add_newdocs_scalars.py

@@ -240,6 +240,18 @@ def add_newdoc_for_scalar_type(obj, fixed_aliases, doc):
     See :ref:`arrays.datetime` for more information.
     """)
 
+add_newdoc('numpy.core.numerictypes', "integer", ('is_integer',
+    f"""
+    integer.is_integer() -> bool
+
+    Return ``True`` if the number is finite with integral value.
+
+    >>> np.int64(-2).is_integer()
+    True
+    >>> np.uint32(5).is_integer()
+    True
+    """))
+
 # TODO: work out how to put this on the base class, np.floating
 for float_name in ('half', 'single', 'double', 'longdouble'):
     add_newdoc('numpy.core.numerictypes', float_name, ('as_integer_ratio',

numpy/core/src/multiarray/scalartypes.c.src

@@ -1937,6 +1937,11 @@ static PyObject *
 }
 /**end repeat**/
 
+static PyObject *
+integer_is_integer(PyObject *self) {
+    Py_RETURN_TRUE;
+}
+
 /*
  * need to fill in doc-strings for these methods on import -- copy from
  * array docstrings
@@ -2195,7 +2200,7 @@ static PyMethodDef @name@type_methods[] = {
 /**end repeat**/
 
 /**begin repeat
- * #name = integer,floating, complexfloating#
+ * #name = floating, complexfloating#
  */
 static PyMethodDef @name@type_methods[] = {
     /* Hook for the round() builtin */
@@ -2206,6 +2211,17 @@ static PyMethodDef @name@type_methods[] = {
 };
 /**end repeat**/
 
+static PyMethodDef integertype_methods[] = {
+    /* Hook for the round() builtin */
+    {"__round__",
+        (PyCFunction)integertype_dunder_round,
+        METH_VARARGS | METH_KEYWORDS, NULL},
+    {"is_integer",
+        (PyCFunction)integer_is_integer,
+        METH_NOARGS, NULL},
+    {NULL, NULL, 0, NULL} /* sentinel */
+};
+
 /**begin repeat
  * #name = half,float,double,longdouble#
  */

numpy/core/tests/test_scalar_methods.py

@@ -104,19 +104,23 @@ def test_roundtrip(self, ftype, frac_vals, exp_vals):
             assert_equal(nf / df, f, "{}/{}".format(n, d))
 
 
-@pytest.mark.parametrize("code", np.typecodes["Float"])
 class TestIsInteger:
     @pytest.mark.parametrize("str_value", ["inf", "nan"])
+    @pytest.mark.parametrize("code", np.typecodes["Float"])
     def test_special(self, code: str, str_value: str) -> None:
         cls = np.dtype(code).type
         value = cls(str_value)
         assert not value.is_integer()
 
+    @pytest.mark.parametrize(
+        "code", np.typecodes["Float"] + np.typecodes["AllInteger"]
+    )
     def test_true(self, code: str) -> None:
         float_array = np.arange(-5, 5).astype(code)
         for value in float_array:
             assert value.is_integer()
 
+    @pytest.mark.parametrize("code", np.typecodes["Float"])
     def test_false(self, code: str) -> None:
         float_array = np.arange(-5, 5).astype(code)
         float_array *= 1.1

numpy/typing/tests/data/reveal/scalars.py

@@ -156,3 +156,5 @@
 if sys.version_info >= (3, 9):
     reveal_type(f8.__ceil__())  # E: int
     reveal_type(f8.__floor__())  # E: int
+
+reveal_type(i8.is_integer())  # E: Literal[True]