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Date: Fri, 08 May 2015 08:04:34 -0400
From: Dave Angel <davea@davea.name>
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Subject: Re: Is this unpythonic?
References: <mailman.224.1431072121.12865.python-list@python.org> <554c8b0a$0$12992$c3e8da3$5496439d@news.astraweb.com> <mii4il$vv$1@ger.gmane.org>
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On 05/08/2015 06:53 AM, Frank Millman wrote:
>
> "Steven D'Aprano" <steve+comp.lang.python@pearwood.info> wrote in message
> news:554c8b0a$0$12992$c3e8da3$5496439d@news.astraweb.com...
>> On Fri, 8 May 2015 06:01 pm, Frank Millman wrote:
>>
>>> Hi all
>>>
> [...]
>>>
>>> However, every time I look at my own code, and I see   "def x(y, z=[]):
>>> ....."   it looks wrong because I have been conditioned to think of it as
>>> a gotcha.
>>

It might be appropriate to define the list at top-level, as

EMPTY_LIST=[]

and in your default argument as
     def x(y, z=EMPTY_LIST):

and with the all-caps, you're thereby promising that nobody will modify 
that list.

(I'd tend to do the None trick, but I think this alternative would be 
acceptable)

-- 
DaveA