bpo-31949: Fixed several issues in printing tracebacks (PyTraceBack_Print()). (#4289)

* Setting sys.tracebacklimit to 0 or less now suppresses printing tracebacks.
* Setting sys.tracebacklimit to None now causes using the default limit.
* Setting sys.tracebacklimit to an integer larger than LONG_MAX now means using
  the limit LONG_MAX rather than the default limit.
* Fixed integer overflows in the case of more than 2**31 traceback items on
  Windows.
* Fixed output errors handling.

Lib/test/test_sys.py

@@ -808,6 +808,39 @@ class SysModuleTest(unittest.TestCase):
         self.assertIsInstance(level, int)
         self.assertGreater(level, 0)
 
+    def test_sys_tracebacklimit(self):
+        code = """if 1:
+            import sys
+            def f1():
+                1 / 0
+            def f2():
+                f1()
+            sys.tracebacklimit = %r
+            f2()
+        """
+        def check(tracebacklimit, expected):
+            p = subprocess.Popen([sys.executable, '-c', code % tracebacklimit],
+                                 stderr=subprocess.PIPE)
+            out = p.communicate()[1]
+            self.assertEqual(out.splitlines(), expected)
+
+        traceback = [
+            b'Traceback (most recent call last):',
+            b'  File "<string>", line 8, in <module>',
+            b'  File "<string>", line 6, in f2',
+            b'  File "<string>", line 4, in f1',
+            b'ZeroDivisionError: division by zero'
+        ]
+        check(10, traceback)
+        check(3, traceback)
+        check(2, traceback[:1] + traceback[2:])
+        check(1, traceback[:1] + traceback[3:])
+        check(0, [traceback[-1]])
+        check(-1, [traceback[-1]])
+        check(1<<1000, traceback)
+        check(-1<<1000, [traceback[-1]])
+        check(None, traceback)
+
 
 @test.support.cpython_only
 class SizeofTest(unittest.TestCase):