function call questions

[chenyong20000 at gmail.com]

在 2016年10月19日星期三 UTC+8上午11:46:28，MRAB写道：
> On 2016-10-19 03:15, chenyong20000 at gmail.com wrote:
> > Thanks Peter and Anssi for your kind help. Now I'm ok with the first question. But the second question still confused me. Why "it seems that
> > after root = root.setdefault(ch,{}) tree['a'] and root are the same
> > object" and follows tree['a']['b']? Thanks.
> >
> You call the .setdefault method with a key and a default value.
> 
> The .setdefault method does this: if the key is in the dict, it returns 
> the associated value, else it puts the key and the default into the dict 
> and then returns the default.

thanks for the reply. I understand this. I'm now confused on why tree got its magic result.