speed up appending integer values to bytearray objects in Py3

Cython/Utility/StringTools.c

@@ -728,6 +728,20 @@ static CYTHON_INLINE int __Pyx_PyByteArray_AppendObject(PyObject* bytearray, PyO
         }
         ival = (unsigned char) (PyString_AS_STRING(value)[0]);
     } else
+#else
+#if CYTHON_USE_PYLONG_INTERNALS
+    if (likely(PyLong_CheckExact(value)) && likely(Py_SIZE(value) == 1 || Py_SIZE(value) == 0)) {
+        if (Py_SIZE(value) == 0) {
+            ival = 0;
+        } else {
+            ival = ((PyLongObject*)value)->ob_digit[0];
+            if (unlikely(ival > 255)) {
+                PyErr_SetString(PyExc_ValueError, "byte must be in range(0, 256)");
+                return -1;
+            }
+        }
+    } else
+#endif
 #endif
     {
         // CPython calls PyNumber_Index() internally

tests/run/bytearraymethods.pyx

@@ -207,6 +207,13 @@ def bytearray_append(bytearray b, signed char c, int i, object o):
     >>> print(b.decode('ascii'))
     abcX@xyz
 
+    >>> b = bytearray(b'abc')
+    >>> b = bytearray_append(b, ord('x'), ord('y'), 0)
+    >>> print(b.decode('ascii')[:-1])
+    abcX@xy
+    >>> b[-1]
+    0
+
     >>> b = bytearray(b'abc')
     >>> b = bytearray_append(b, ord('x'), ord('y'), ord('z') if IS_PY3 else b'z')
     >>> print(b.decode('ascii'))