don't understand behaviour of recursive structure

[MRAB]

Dan Davison wrote:
> I'm new to python. Could someone please explain the following behaviour
> of a recursive data structure?
> 
> def new_node(id='', daughters=[]):
>     return dict(id=id, daughters=daughters)
> 
> n0 = new_node(id='n0')
> n1 = new_node(id='n1')
> 
[snip]
See 
http://www.python.org/doc/faq/general/#why-are-default-values-shared-between-objects