support default argument in next built-in function (#131)

Fixes TypeError: guarded_next() takes exactly 1 argument (2 given) when using next(iter, default) in restricted environment.

CHANGES.rst

@@ -7,6 +7,7 @@ For changes before version 3.0, see ``HISTORY.rst``.
 ----------------
 
 - Add support for Python 3.11 (as of 3.11.0a6).
+- Support ``default`` argument in ``next`` built-in function.
 
 
 5.3.1 (2022-03-29)

src/AccessControl/ZopeGuards.py

@@ -254,8 +254,11 @@ def _check_list_access(name, value):
 # iterator that is known to be safe (as in guarded_enumerate).
 
 
-def guarded_next(iterator):
-    ob = next(iterator)
+def guarded_next(iterator, default=_marker):
+    if default is _marker:
+        ob = next(iterator)
+    else:
+        ob = next(iterator, default)
     if not isinstance(iterator, SafeIter):
         guard(ob, ob)
     return ob

src/AccessControl/tests/testZopeGuards.py

@@ -878,6 +878,37 @@ def test_guarded_next__1(self):
 
         self.assertEqual(its_globals['result'], 2411)
 
+    def test_guarded_next_default(self):
+        """There is a `safe_builtin` named `next` with `default`."""
+        SCRIPT = "result = next(iterator, 'default')"
+
+        code, its_globals = self._compile_str(SCRIPT, 'ignored')
+        its_globals['iterator'] = iter([])
+
+        sm = SecurityManager()
+        old = self.setSecurityManager(sm)
+        try:
+            exec(code, its_globals)
+        finally:
+            self.setSecurityManager(old)
+        self.assertEqual(its_globals['result'], "default")
+
+    def test_guarded_next_StopIteration(self):
+        """There is a `safe_builtin` named `next`, raising StopIteration
+        when iterator is exhausted."""
+        SCRIPT = "result = next(iterator)"
+
+        code, its_globals = self._compile_str(SCRIPT, 'ignored')
+        its_globals['iterator'] = iter([])
+
+        sm = SecurityManager()
+        old = self.setSecurityManager(sm)
+        with self.assertRaises(StopIteration):
+            try:
+                exec(code, its_globals)
+            finally:
+                self.setSecurityManager(old)
+
     def test_guarded_next__2(self):
         """It guards the access during iteration."""
         from AccessControl import Unauthorized