"Johannes Bauer" <dfnsonfsdu...@gmx.de> wrote in message news:min3f0$2gh$1...@news.albasani.net... On 08.05.2015 14:04, Dave Angel wrote:
> > 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 think it's a really bad idea to use a module-global mutable > "EMPTY_LIST". It's much too easy this happens: > # Globally > >>> EMPTY_LIST = [ ] > # At somewhere in the code at some point in time > >>> foo = EMPTY_LIST > >>> foo.append(123) > >>> print(foo) > [123] > # Some other place in code > >>> bar = EMPTY_LIST > >>> print(bar) > [123] A fair point. How about this as an alternative? If one were to use this technique at all, it would be necessary to add a comment at the top explaining the reason for this odd declaration. It is then a simple extra step to say - EMPTY_L:IST = () and if required - EMPTY_DICT = () and expand the explanation to show why a tuple is used instead. So if there was a situation where the overhead of testing for None became a problem, this solution offers the following - 1. it solves the 'overhead' problem 2. it reads reasonably intuitively in the body of the program 3. it is safe 4. it should not be difficult to write a suitable self-explanatory comment Frank -- https://mail.python.org/mailman/listinfo/python-list
