bpo-40795: ctypes calls unraisablehook with an exception (GH-20452)

If ctypes fails to convert the result of a callback or if a ctypes
callback function raises an exception, sys.unraisablehook is now
called with an exception set. Previously, the error was logged into
stderr by PyErr_Print().

Lib/ctypes/test/test_callbacks.py

@@ -1,5 +1,7 @@
 import functools
 import unittest
+from test import support
+
 from ctypes import *
 from ctypes.test import need_symbol
 import _ctypes_test
@@ -301,8 +303,22 @@ class SampleCallbacksTestCase(unittest.TestCase):
         with self.assertRaises(ArgumentError):
             cb(*args2)
 
+    def test_convert_result_error(self):
+        def func():
+            return ("tuple",)
+
+        proto = CFUNCTYPE(c_int)
+        ctypes_func = proto(func)
+        with support.catch_unraisable_exception() as cm:
+            # don't test the result since it is an uninitialized value
+            result = ctypes_func()
+
+            self.assertIsInstance(cm.unraisable.exc_value, TypeError)
+            self.assertEqual(cm.unraisable.err_msg,
+                             "Exception ignored on converting result "
+                             "of ctypes callback function")
+            self.assertIs(cm.unraisable.object, func)
 
-################################################################
 
 if __name__ == '__main__':
     unittest.main()

Lib/ctypes/test/test_random_things.py

@@ -1,5 +1,9 @@
 from ctypes import *
-import unittest, sys
+import contextlib
+from test import support
+import unittest
+import sys
+
 
 def callback_func(arg):
     42 / arg
@@ -34,41 +38,40 @@ class CallbackTracbackTestCase(unittest.TestCase):
     # created, then a full traceback printed.  When SystemExit is
     # raised in a callback function, the interpreter exits.
 
-    def capture_stderr(self, func, *args, **kw):
-        # helper - call function 'func', and return the captured stderr
-        import io
-        old_stderr = sys.stderr
-        logger = sys.stderr = io.StringIO()
-        try:
-            func(*args, **kw)
-        finally:
-            sys.stderr = old_stderr
-        return logger.getvalue()
+    @contextlib.contextmanager
+    def expect_unraisable(self, exc_type, exc_msg=None):
+        with support.catch_unraisable_exception() as cm:
+            yield
+
+            self.assertIsInstance(cm.unraisable.exc_value, exc_type)
+            if exc_msg is not None:
+                self.assertEqual(str(cm.unraisable.exc_value), exc_msg)
+            self.assertEqual(cm.unraisable.err_msg,
+                             "Exception ignored on calling ctypes "
+                             "callback function")
+            self.assertIs(cm.unraisable.object, callback_func)
 
     def test_ValueError(self):
         cb = CFUNCTYPE(c_int, c_int)(callback_func)
-        out = self.capture_stderr(cb, 42)
-        self.assertEqual(out.splitlines()[-1],
-                             "ValueError: 42")
+        with self.expect_unraisable(ValueError, '42'):
+            cb(42)
 
     def test_IntegerDivisionError(self):
         cb = CFUNCTYPE(c_int, c_int)(callback_func)
-        out = self.capture_stderr(cb, 0)
-        self.assertEqual(out.splitlines()[-1][:19],
-                             "ZeroDivisionError: ")
+        with self.expect_unraisable(ZeroDivisionError):
+            cb(0)
 
     def test_FloatDivisionError(self):
         cb = CFUNCTYPE(c_int, c_double)(callback_func)
-        out = self.capture_stderr(cb, 0.0)
-        self.assertEqual(out.splitlines()[-1][:19],
-                             "ZeroDivisionError: ")
+        with self.expect_unraisable(ZeroDivisionError):
+            cb(0.0)
 
     def test_TypeErrorDivisionError(self):
         cb = CFUNCTYPE(c_int, c_char_p)(callback_func)
-        out = self.capture_stderr(cb, b"spam")
-        self.assertEqual(out.splitlines()[-1],
-                             "TypeError: "
-                             "unsupported operand type(s) for /: 'int' and 'bytes'")
+        err_msg = "unsupported operand type(s) for /: 'int' and 'bytes'"
+        with self.expect_unraisable(TypeError, err_msg):
+            cb(b"spam")
+
 
 if __name__ == '__main__':
     unittest.main()

Lib/ctypes/test/test_unaligned_structures.py

@@ -27,7 +27,6 @@ for typ in [c_short, c_int, c_long, c_longlong,
 class TestStructures(unittest.TestCase):
     def test_native(self):
         for typ in structures:
-##            print typ.value
             self.assertEqual(typ.value.offset, 1)
             o = typ()
             o.value = 4
@@ -35,7 +34,6 @@ class TestStructures(unittest.TestCase):
 
     def test_swapped(self):
         for typ in byteswapped_structures:
-##            print >> sys.stderr, typ.value
             self.assertEqual(typ.value.offset, 1)
             o = typ()
             o.value = 4