Problem with shelve / nested lists

[Michael Schmitt]

Hello.
I'm trying to use a shelve as a disc based dictionary, but have problems 
with nested lists. If I store a nested list as value, inner lists seem to 
be immutable.

According to the library reference, shelves can store "essentially 
arbitrary Python objects" and "recursive data types".

What is my misunderstanding?

Python2.2:
>>> import shelve
>>> d1= shelve.open('dict.dat','c')
>>> d1['bla']= [1,2,[10,20]]
>>> d1['bla'][2]
[10, 20]
>>> d1['bla'][2].append(30)
>>> d1['bla'][2]
[10, 20]


Using a dictionary instead of the shelve, lets append to the inner list.
>>> d2= {}
>>> d2['bla']= [1,2,[10,20]]
>>> d2['bla'][2]
[10, 20]
>>> d2['bla'][2].append(30)
>>> d2['bla'][2]
[10, 20, 30]


Thanks for any hint, 
Michael