[Zope] Modifying a Dictionaries in an Extenal Method

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Zopistas:

Does Zope allos an external method to modify a dictionary object that
is passed to the external method via the REQUEST object.

I am working with the object:

items_list = [{'element1':'element1value',
'element2':'element2value','element3': element3value},{....},....]

I am getting trouble with with this as  any time I try to modify any
dictionary  from items_list,  items_list[n]   I do get an error
similar to:

 line 120, in agregaItemDicts def agregaItemLista2(self,item,REQUEST):
File "/usr/local/Zope-2.7.4/lib/python/ZPublisher/HTTPRequest.py",
line 1502, in __getattr__ raise AttributeError, key AttributeError:
__setitem__

It looks like the dictionary is behaving as if it not were a mutable
object (as it is in Python),  I have no trouble modifying the  list
'items_list' itself.

i have read a bit about dictionaries persistence and calling  
_p_changed=1   bu have not had any luck so far.   I am using an
external method, not a product.

Any ideas would be appreciated..

Best regards.