Add with statement support for old style classes

and let the interpreter actually do a cls lookup when encountering a ClsAttribute node...

src/codegen/ast_interpreter.cpp

@@ -484,7 +484,7 @@ Value ASTInterpreter::visit_invoke(AST_Invoke* node) {
 }
 
 Value ASTInterpreter::visit_clsAttribute(AST_ClsAttribute* node) {
-    return getattr(visit_expr(node->value).o, node->attr.c_str());
+    return getclsattr(visit_expr(node->value).o, node->attr.c_str());
 }
 
 Value ASTInterpreter::visit_augBinOp(AST_AugBinOp* node) {

src/runtime/objmodel.cpp

@@ -1207,6 +1207,13 @@ extern "C" Box* getclsattr(Box* obj, const char* attr) {
 
     Box* gotten;
 
+    if (attr[0] == '_' && attr[1] == '_' && PyInstance_Check(obj)) {
+        // __enter__ and __exit__ need special treatment.
+        static std::string enter_str("__enter__"), exit_str("__exit__");
+        if (attr == enter_str || attr == exit_str)
+            return getattr(obj, attr);
+    }
+
 #if 0
     std::unique_ptr<Rewriter> rewriter(Rewriter::createRewriter(__builtin_extract_return_addr(__builtin_return_address(0)), 2, 1, "getclsattr"));
 
@@ -2508,6 +2515,12 @@ extern "C" Box* callattr(Box* obj, const std::string* attr, CallattrFlags flags,
 
     LookupScope scope = flags.cls_only ? CLASS_ONLY : CLASS_OR_INST;
 
+    if ((*attr)[0] == '_' && (*attr)[1] == '_' && PyInstance_Check(obj)) {
+        // __enter__ and __exit__ need special treatment.
+        if (*attr == "__enter__" || *attr == "__exit__")
+            scope = CLASS_OR_INST;
+    }
+
     if (rewriter.get()) {
         // TODO feel weird about doing this; it either isn't necessary
         // or this kind of thing is necessary in a lot more places

test/tests/with_exit.py

 # Make sure __exit__ gets called in various exit scenarios:
 
-class C(object):
+class NewC(object):
     def __enter__(self):
         print "__enter__"
     def __exit__(self, type, val, tb):
         print "__exit__"
 
-def f():
+
+class OldC:
+    def __enter__(self):
+        print "__enter__"
+    def __exit__(self, type, val, tb):
+        print "__exit__"
+
+def f(C):
     with C():
         pass
     with C() as n:
@@ -42,9 +49,10 @@ def f():
         with C() as o:
             return
 
-f()
+f(NewC)
+f(OldC)
 
-def f2(b):
+def f2(b, C):
     n = 2
     while n:
         print n
@@ -56,6 +64,6 @@ def f2(b):
                 else:
                     return "b false"
 
-print f2(False)
-print f2(True)
+print f2(False, NewC), f2(False, OldC)
+print f2(True, NewC), f2(True, OldC)