python · ndessart · Feb 18, 2020
diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
@@ -3,7 +3,7 @@
 import os as _os, sys as _sys
 import types as _types
 
-__version__ = "1.1.0"
+__version__ = "1.1.1"
 
 from _ctypes import Union, Structure, Array
 from _ctypes import _Pointer
@@ -560,4 +560,18 @@ def DllCanUnloadNow():
     elif sizeof(kind) == 8: c_uint64 = kind
 del(kind)
 
+# _ctypes needs the following types for variadic function type promotion
+import _ctypes
+_ctypes.c_int = c_int
+_ctypes.c_uint = c_uint
+_ctypes.c_int8 = c_int8
+_ctypes.c_uint8 = c_uint8
+_ctypes.c_int16 = c_int16
+_ctypes.c_uint16 = c_uint16
+_ctypes.c_int32 = c_int32
+_ctypes.c_uint32 = c_uint32
+_ctypes.c_int64 = c_int64
+_ctypes.c_uint64 = c_uint64
+_ctypes.c_double = c_double
+
 _reset_cache()
diff --git a/Lib/ctypes/test/test_functions.py b/Lib/ctypes/test/test_functions.py
@@ -138,6 +138,47 @@ def test_doubleresult(self):
         self.assertEqual(result, -21)
         self.assertEqual(type(result), float)
 
+    def test_doubleresult_var(self):
+        f = dll._testfunc_d_bhilfd_var
+        # This function only supports the following argument types:
+        # c_byte, c_short, c_int, c_long, c_float, c_double
+        # Even if it's a variadic function, don't try to pass anything else
+        f.argtypes = (c_int, ...)
+        f.restype = c_double
+
+        # builtin types
+        result = f(0, 1, 2, 3, 4, 5.0, 6.0)
+        self.assertEqual(result, 21)
+        self.assertEqual(type(result), float)
+
+        # user defined types with _as_parameter_
+        class AsParameter:
+            def __init__(self, number):
+                self._as_parameter_ = number
+        result = f(0, *map(AsParameter, (1, 2, 3, 4, 5.0, 6.0)))
+        self.assertEqual(result, 21)
+        self.assertEqual(type(result), float)
+
+        # ctypes without automatic type promotion
+        result = f(
+            0, c_int(1), c_int(2), c_int(3), c_int(4), c_double(5.0),
+            c_double(6.0)
+        )
+        self.assertEqual(result, 21)
+        self.assertEqual(type(result), float)
+
+        # ctypes with automatic type promotion
+        result = f(
+            0, c_byte(1), c_int8(2 ** 7 - 1), c_uint32(2 ** 32 - 1),
+            c_int32(4), c_float(5.0), c_double(6.0)
+        )
+        self.assertEqual(result, 1 + 2 ** 7 - 1 - 1 + 4 + 5. + 6.)
+        self.assertEqual(type(result), float)
+
+        result = f(0, -1, -2, -3, -4, -5.0, -6.0)
+        self.assertEqual(result, -21)
+        self.assertEqual(type(result), float)
+
     def test_longdoubleresult(self):
         f = dll._testfunc_D_bhilfD
         f.argtypes = [c_byte, c_short, c_int, c_long, c_float, c_longdouble]

diff --git a/Lib/ctypes/test/test_python_api.py b/Lib/ctypes/test/test_python_api.py
@@ -68,7 +68,7 @@ def test_PyObj_FromPtr(self):
 
     def test_PyOS_snprintf(self):
         PyOS_snprintf = pythonapi.PyOS_snprintf
-        PyOS_snprintf.argtypes = POINTER(c_char), c_size_t, c_char_p
+        PyOS_snprintf.argtypes = POINTER(c_char), c_size_t, c_char_p, ...
 
         buf = c_buffer(256)
         PyOS_snprintf(buf, sizeof(buf), b"Hello from %s", b"ctypes")

diff --git a/Misc/NEWS.d/next/Library/2020-02-19-11-56-22.bpo-39632.7jCbTV.rst b/Misc/NEWS.d/next/Library/2020-02-19-11-56-22.bpo-39632.7jCbTV.rst
@@ -0,0 +1,6 @@
+Fix and improve ctypes variadic function support. Functions that take a
+variable number of arguments should now be declared using an Ellipsis (...)
+as their last argument (just as a prototype for a C function).  ctypes variadic
+functions declared this way automatically perform the default argument
+promotion (small integer types are promoted to c_int and c_float is promoted to
+double).