On Fri, May 8, 2015 at 6:01 PM, Frank Millman <fr...@chagford.com> wrote: > I have often read about the gotcha regarding 'mutable default arguments' > that frequently trips people up. > > I use them from time to time, but I have never had a problem. I have just > delved a bit deeper to see if I am skating on thin ice. > > AFAICT my usage is safe. If I use a list as an argument, I only use it to > pass values *into* the function, but I never modify the list. So if I omit > the argument, the original default empty list is used, otherwise the list > that I pass in is used.
In that case, you may want to consider using a default of () rather than [], unless there's some reason that it has to be a list. With a tuple, you have a guarantee that it's not going to be changed, so it's as safe as a default argument of True or 42 or "Hello". That may or may not help, but it's worth considering, especially if all you really need is an iterable (or a sequence). ChrisA -- https://mail.python.org/mailman/listinfo/python-list
