Chris Rebert <cvrebert@gmail.com> wrote:
If A.M. Kuchling's list of Python Warts is any indication, Python has removed many of the warts it once had. However, the behavior of mutable default argument values is still a frequent stumbling-block for newbies. It is also present on at least 3 different lists of Python's deficiencies ([0][1][2]).
Example of current, unintuitive behavior (snipped from [0]):
def popo(x=[]): ... x.append(666) ... print x ... popo() [666] popo() [666, 666] popo() [666, 666, 666] [snip] Comments?
As provided by Calvin Spealman, the above can be fixed with: def popo(x=None): x = x if x is not None else [] x.append(666) print x I would also mention that forcing users to learn about mutable arguments and procedural programming is not a bad thing. Learning the "gotcha" of mutable default arguments is a very useful lesson, and to remove that lesson, I believe, wouldn't necessarily help new users to Python, or new programmers in general. - Josiah