I have no problem of making my programme run properly (asking first if in dict etc), but I just read the docu of dict.setdefault

setdefault(key[, default]) 
If key is in the dictionary, return its value. If not, insert key with a value of default and return default. default defaults to None.

and it clearly reads if the key is.. return its value, with a full stop;
so either the docu is wrong (but proposes exactly the needed shortcut) or python is as it is: come in & find out