Is this unpythonic?

Sat May 9 02:51:40 EDT 2015

"Frank Millman" <frank at chagford.com> wrote in message 
news:mik7j659ドルn$1 at ger.gmane.org...
>> "Steven D'Aprano" <steve+comp.lang.python at pearwood.info> wrote in message 
> news:554cd1190ドル12977ドル$c3e8da3$5496439d at news.astraweb.com...
>> On Fri, 8 May 2015 08:53 pm, Frank Millman wrote:
>>>>>> Does z have to be a list? Could you use an empty tuple instead?
>>>>>>>> def x(y, z=()): ...
>>>>>>>>>> That was Chris' suggestion as well (thanks Chris).
>>>>>> The idea appealed to me, but then I found a situation where I pass in a
>>> dictionary instead of a list, so that would not work.
>>>>>> Why wouldn't it work? If it worked with an empty list, it will probably 
>> work
>> with an empty tuple instead.
>>>> Sorry, I should have been more explicit. In the case of a dictionary, I 
> used 'def x(y, z={}'
>> I have not checked, but I assume that as dictionaries are mutable, this 
> suffers from the same drawback as a default list.
>> Unlike a list, it cannot be replaced by an empty tuple without changing 
> the body of the function.
>> Dave's suggestion would have worked here -
>> EMPTY_LIST = []
> EMPTY_DICT = {}
>> But as I have decided to use the None trick, I use it for a default 
> dictionary as well.
>
Cough, cough, I really should have given that a moment's thought before 
posting.
It just dawned on me that a dictionary *can* be replaced by an empty tuple 
without changing the body of the function.
There are two operations I might perform on the dictionary -
1. iterate over the keys and retrieve the values
2: use 'in' to test if a given string exists as a key
Both of these operations will work on a tuple and give the desired result, 
so it is a very valid workaround.
More testing needed ...
Frank