On Sun, Oct 4, 2009 at 2:29 AM, horos11 <horo...@gmail.com> wrote: > All, > > Another one, this time a bit shorter. > > It looks like defaults for arguments are only bound once, and every > subsequent call reuses the first reference created. Hence the > following will print '[10,2]' instead of the expected '[1,2]'. > > Now my question - exactly why is 'default_me()' only called once, on > the construction of the first object? And what's the best way to get > around this if you want to have a default for an argument which so > happens to be a reference or a new object?
This is a FAQ: http://www.python.org/doc/faq/general/#why-are-default-values-shared-between-objects > > ---- code begins here --- > > import copy > class A: > > def default_me(): > return [1,2] > > def __init__(self, _arg=default_me()): > self.arg = _a > > > a = A() > a.arg[0] = 10 > b = A() > > print b.arg # prints [10,2] Your code is weird: you import copy module but don't use it; you define default_me() as a "sort of" static method (http://docs.python.org/library/functions.html#staticmethod) but then only use it to generate a default argument that has nothing to do with the class you just defined; and in __init__() you use "_a" which isn't defined anywhere in this code snippet. What are you actually trying to accomplish? -- http://mail.python.org/mailman/listinfo/python-list
