Peter Otten wrote: > Kay Schluehr wrote: > > > I want to manipulate a deeply nested list in a generic way at a > > determined place. Given a sequence of constant objects a1, a2, ..., aN > > and a variable x. Now construct a list from them recursively: > > > > L = [a1, [a2, [....[aN, [x]]...]] > > > > The value of x is the only one to be changed. With each value of x a > > new instance of L is needed so that we actually have a function: > > > > L = lambda x: [a1, [a2, [....[aN, [x]]...]] > > > > I'm seeking for an efficient implementation that does not recompute the > > whole list each time. Any ideas? > > I'd say you are nesting the wrong way.
The structure of the sequence is *not* optional. > > >>> items = make_list(range(10)) > >>> def make_list(items): > ... return reduce(lambda *args: args, items) > ... > >>> def update_value(items, value): > ... return items[0], value > ... > >>> items = make_list(range(10)) > >>> items > (((((((((0, 1), 2), 3), 4), 5), 6), 7), 8), 9) > >>> update_value(items, 42) > (((((((((0, 1), 2), 3), 4), 5), 6), 7), 8), 42) > > Obviously I must be missing something. What? The structure of the sequence is *not* optional. Of course you can also take the original sequence and apply: >>> L = list([a1, [a2, [....[aN, [x]]...]]) # shallow copy >>> L[0] = b but it is intended to change the most inner element. I guess there is no way in doing it without a deepcopy / full list construction. Kay -- http://mail.python.org/mailman/listinfo/python-list
