[python] check for 'item not in mylist' causes TestComplete to crash

I am trying to build a list of backpointers. In there, I want to avoid duplicates. As far as i know i cant use a dict or set, because the items to be stored are not hashable. I implented the following code:

while k in range(limit):
    try:
        if path not in path_backp:
            path_backp.append(path)
            continue
        else:
            Log.Message(path.Item[k].Text)
            path = path.Item[k].Items
            limit = path.Count                
            scan(path, path_backp, e, 0)
            k = k +1
    except AttributeError:
        path = path_backp.pop()
        limit = path.Count
        k = k + 1

the part to avoid double entities of course is:

if path not in path_backp:
     path_backp.append(path)
     continue
else:
     [...]

Im running python inside TestComplete, which has (limited) debugging functions. When I enable the debugger and track what is happening, the first check works. The if-routine gets executed, and because path_backp is an empty dict, path gets appended, so that afterwards path_backp[0] equals path and I get back to to the while-routine. But when the if-routine gets executed the 2nd time (so when path_backp is no empty dict anymore), the debugger freezes for what seems an infinite amount of time.

same happens, by the way, when I implemented:

if path not in path_backp:    
 path_backp.append(path)

without any continue or else.

Can anyone explain to me why this is happening and how I can handle the situation?

Many thanks,

t.