Let interfaces be iterated on Python 3

Fixes zopefoundation/zope.interface#141

CHANGES.rst

@@ -2,14 +2,16 @@
  Changes
 =========
 
-5.1 (unreleased)
-================
+5.1.0 (unreleased)
+==================
 
-- Nothing changed yet.
+- Let proxied interfaces be iterated on Python 3. This worked on
+  Python 2, but raised ``ForbiddenAttribute`` an Python 3. See
+  `zope.interface issue 141 <https://github.com/zopefoundation/zope.interface/issues/141>`_.
 
 
-5.0 (2019-11-11)
-================
+5.0.0 (2019-11-11)
+==================
 
 - Drop support for Python 3.4.
 

setup.py

@@ -132,7 +132,7 @@ def __str__(self):
 
 
 setup(name='zope.security',
-      version='5.1.dev0',
+      version='5.1.0.dev0',
       author='Zope Foundation and Contributors',
       author_email='zope-dev@zope.org',
       description='Zope Security Framework',

src/zope/security/checker.py

@@ -858,8 +858,14 @@ def f(): # pragma: no cover
     type(f()): _iteratorChecker,
     type(Interface): InterfaceChecker(
         IInterface,
-        __str__=CheckerPublic, _implied=CheckerPublic, subscribe=CheckerPublic,
-        ),
+        __str__=CheckerPublic,
+        _implied=CheckerPublic,
+        subscribe=CheckerPublic,
+        # To iterate, Python calls __len__ as a hint.
+        # Python 2 ignores AttributeErrors, but Python 3
+        # lets them pass.
+        __len__=CheckerPublic,
+    ),
     zope.interface.interface.Method: InterfaceChecker(
         zope.interface.interfaces.IMethod),
     zope.interface.declarations.ProvidesClass: _Declaration_checker,

src/zope/security/tests/test_proxy.py

@@ -27,6 +27,7 @@ def coerce(*args):
         raise NotImplementedError("Not on Python 3")
     cmp = coerce
     long = int
+    unicode = str
 
 class AbstractProxyTestBase(object):
 
@@ -1770,7 +1771,7 @@ def __contains__(self, x):
         return x == 42
 
 
-class ProxyTests(unittest.TestCase):
+class ProxyFactoryTests(unittest.TestCase):
 
     def setUp(self):
         from zope.security.proxy import ProxyFactory
@@ -1958,6 +1959,11 @@ class C(object):
     if PYTHON2:
         unops.append("long(x)")
 
+    def _make_eval(self, expr, locs):
+        def _eval(*args):
+            eval(expr, globals(), locs)
+        return _eval
+
     def test_unops(self):
         # We want the starting value of the expressions to be a proxy,
         # but we don't want to create new proxies as a result of
@@ -1968,6 +1974,7 @@ def test_unops(self):
         self.c.unproxied_types = {str, int, float}
         if PYTHON2:
             self.c.unproxied_types.add(long)
+
         for expr in self.unops:
             x = 1
             y = eval(expr)
@@ -1976,7 +1983,7 @@ def test_unops(self):
             z = eval(expr)
             self.assertEqual(removeSecurityProxy(z), y,
                              "x=%r; expr=%r" % (x, expr))
-            self.shouldFail(lambda x: eval(expr), x)
+            self.shouldFail(self._make_eval(expr, locals()), x)
 
     @_skip_if_not_Py2
     def test_odd_unops(self):
@@ -2007,7 +2014,7 @@ def test_binops(self):
                     else:
                         self.assertEqual(removeSecurityProxy(eval(expr)), z,
                                          "x=%r; y=%r; expr=%r" % (x, y, expr))
-                        self.shouldFail(lambda x, y: eval(expr), x, y)
+                        self.shouldFail(self._make_eval(expr, locals()), x, y)
 
     def test_inplace(self):
         # TODO: should test all inplace operators...
@@ -2101,6 +2108,20 @@ def test_coerce(self):
         self.assertIs(type(removeSecurityProxy(a)), float)
         self.assertIs(b, y)
 
+    def test_iterate_interface(self):
+        # This used to work on Python 2, but fail on Python 3.
+        # See https://github.com/zopefoundation/zope.interface/issues/141
+        from zope.interface import Interface
+        from zope.security.proxy import ProxyFactory
+
+        class IFoo(Interface):
+            def x():
+                """A method"""
+
+        proxy = ProxyFactory(IFoo)
+        self.assertEqual(list(IFoo), ['x'])
+        self.assertEqual(list(proxy), list(IFoo))
+
 
 def test_using_mapping_slots_hack():
     """The security proxy will use mapping slots, on the checker to go faster