diff --git a/IPython/extensions/autoreload.py b/IPython/extensions/autoreload.py
index 5bd38b3..353124a 100644
--- a/IPython/extensions/autoreload.py
+++ b/IPython/extensions/autoreload.py
@@ -268,66 +268,14 @@ def update_function(old, new):
             pass
 
 
-def _find_instances(old_type):
-    """Try to find all instances of a class that need updating.
-
-    Classic graph exploration, we want to avoid re-visiting object multiple times.
-    """
-    # find ipython workspace stack frame, this is just to bootstrap where we
-    # find the object that need updating.
-    frame = next(frame_nfo.frame for frame_nfo in inspect.stack()
-                 if 'trigger' in frame_nfo.function)
-    # build generator for non-private variable values from workspace
-    shell = frame.f_locals['self'].shell
-    user_ns = shell.user_ns
-    user_ns_hidden = shell.user_ns_hidden
-    nonmatching = object()
-    objects = ( value for key, value in user_ns.items()
-            if not key.startswith('_')
-            and (value is not user_ns_hidden.get(key, nonmatching))
-            and not inspect.ismodule(value))
-
-    # note:  in the following we do use dict as object might not be hashable.
-    # list of objects we found that will need an update.
-    to_update = {}
-
-    # list of object we have not recursed into yet
-    open_set = {}
-
-    # list of object we have visited already
-    closed_set = {}
-
-    open_set.update({id(o):o for o in objects})
-
-    it = 0
-    while len(open_set) > 0:
-        it += 1
-        if it > 100_000:
-            raise ValueError('infinite')
-        (current_id,current) =  next(iter(open_set.items()))
-        if type(current) is old_type:
-            to_update[current_id] = current
-        if hasattr(current, '__dict__') and not (inspect.isfunction(current)
-                                                 or inspect.ismethod(current)):
-            potential_new = {id(o):o for o in current.__dict__.values() if id(o) not in closed_set.keys()}
-            open_set.update(potential_new)
-        # if object is a container, search it
-        if hasattr(current, 'items') or (hasattr(current, '__contains__')
-                                         and not isinstance(current, str)):
-            potential_new = (value for key, value in current.items()
-                       if not str(key).startswith('_')
-                       and not inspect.ismodule(value) and not id(value) in closed_set.keys())
-            open_set.update(potential_new)
-        del open_set[id(current)]
-        closed_set[id(current)] = current
-    return to_update.values()
-
-def update_instances(old, new, objects=None):
+def update_instances(old, new, objects=None, visited={}):
     """Iterate through objects recursively, searching for instances of old and
     replace their __class__ reference with new. If no objects are given, start 
     with the current ipython workspace.
     """
-    if not objects:
+    if objects is None:
+        # make sure visited is cleaned when not called recursively
+        visited = {}
         # find ipython workspace stack frame
         frame = next(frame_nfo.frame for frame_nfo in inspect.stack() 
                      if 'trigger' in frame_nfo.function)
@@ -349,7 +297,9 @@ def update_instances(old, new, objects=None):
 
     # try if objects is iterable
     try:
-        for obj in objects:
+        for obj in (obj for obj in objects if id(obj) not in visited):
+            # add current object to visited to avoid revisiting
+            visited.update({id(obj):obj})
 
             # update, if object is instance of old_class (but no subclasses)
             if type(obj) is old:
@@ -359,21 +309,21 @@ def update_instances(old, new, objects=None):
             # if object is instance of other class, look for nested instances
             if hasattr(obj, '__dict__') and not (inspect.isfunction(obj)
                                                  or inspect.ismethod(obj)):
-                update_instances(old, new, obj.__dict__)
+                update_instances(old, new, obj.__dict__, visited)
 
             # if object is a container, search it
             if hasattr(obj, 'items') or (hasattr(obj, '__contains__')
                                          and not isinstance(obj, str)):
-                update_instances(old, new, obj)
+                update_instances(old, new, obj, visited)
 
     except TypeError:
         pass
 
-        
+
 def update_class(old, new):
     """Replace stuff in the __dict__ of a class, and upgrade
     method code objects, and add new methods, if any"""
-    print('old is', old)
+    print('old is', id(old))
     for key in list(old.__dict__.keys()):
         old_obj = getattr(old, key)
         try:
@@ -405,8 +355,7 @@ def update_class(old, new):
                 pass # skip non-writable attributes
 
     # update all instances of class
-    for instance in _find_instances(old):
-        instance.__class__ = new
+    update_instances(old, new)
 
 
 def update_property(old, new):