[Zope] Persistent variable in Python Script? Is this a feature or a bug?

Given a Python Script A which only returns an array ======== return ('a') ======== Then call A in another Python Script B with parameter list: b=[] ======== b.append(container.A()) return b ======== Then request B in browser. Guess what happened? ['a'] correct! But what if you "reload" B again and again? You will get ['a','a','a',........] Well, why this happen? A feature or A bug? I thought that the parameter should be cleared at each new request. How to get a "local" parameter without this persistent feature? Any idea? Thanks a lot. Iap, Singuan