On Aug 22, 11:13 am, Bart van Deenen <[EMAIL PROTECTED]> wrote: > Hi all. > > I've stumbled onto a python behavior that I don't understand at all. > > Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) > > # function > def X(l=[]): > l.append(1) > print l > > # first call of X > X() > [1] > > #second call of X > X() > [1, 1] > > Where does the list parameter 'l' live between the two successive calls of > X(). > Why is it not recreated with an empty list? > Is this correct behavior or is it a Python bug? > Does anyone have any pointers to the language documentation where this > behavior is described? > > Thanks all > > Bart van Deenen
http://docs.python.org/ref/function.html "Default parameter values are evaluated when the function definition is executed." Depending on your use the common way to handle this is to do def x(lst = None): if lst is None: pass # lst has not been set to anything else: pass # lst has been set to something -- http://mail.python.org/mailman/listinfo/python-list
