implemented __next__ method

evaluate.py

@@ -17,7 +17,7 @@ TODO nonlocal statement
 TODO __ instance attributes should not be visible outside of the class.
 TODO getattr / __getattr__ / __getattribute__ ?
 """
-from _compatibility import next, property, hasattr
+from _compatibility import next, property, hasattr, is_py3k
 
 import sys
 import itertools
@@ -939,7 +939,7 @@ def get_scopes_for_name(scope, name_str, position=None, search_global=False):
                     try:
                         generators += it.execute_subscope_by_name('__iter__')
                     except KeyError:
-                        pass
+                        debug.warning('`for r in x`: x has no __iter__ method')
 
             result = []
             for gen in generators:
@@ -948,6 +948,13 @@ def get_scopes_for_name(scope, name_str, position=None, search_global=False):
                     # array, but there's also the list builtin, which is
                     # another thing.
                     in_vars = gen.get_index_types()
+                elif isinstance(gen, Instance):
+                    # __iter__ returned an instance.
+                    name = '__next__' if is_py3k() else 'next'
+                    try:
+                        in_vars = it.execute_subscope_by_name(name)
+                    except KeyError:
+                        debug.warning('Instance has no __next__ function', gen)
                 else:
                     # is a generator
                     in_vars = gen.get_content()