Puzzled by list-appending behavior

[Steven D'Aprano]

On Thu, 26 May 2011 11:27:35 -0700, John Ladasky wrote:

> On May 25, 9:46 pm, Uncle Ben <bgr... at nycap.rr.com> wrote:
> 
>> list = [1,2,3]
> 
> Somewhat unrelated, but... is it a good idea to name your list "list"? 
> Isn't that the name of Python's built-in list constructor method?
> 
> Shadowing a built-in has contributed to more than one subtle bug in my
> code, and I've learned to avoid it.

Agreed. However, there are good reasons for sometimes shadowing built-
ins, and namespaces make it safe to do so if you are sufficiently careful.

E.g. I have a module stats.sum() which shadows the built-in, but only in 
that module, which is exactly the behaviour I want. 

(If you do "from stats import sum", then you're responsible for whatever 
happens next.)

Or you might isolate the shadow to a function small enough that you can 
be sure that it won't cause any problems, e.g.:

def get(list, object):
    """Append object to a copy of list and return it."""
    return list + [object]

For one or two line functions, I think that's perfectly reasonable. 
Anything more than that, I'd be getting nervous.


-- 
Steven