Mutable default arguments don't mutate

[David K. Zhang]

def foo(xs=[]):
    xs.append(5)
    return xs

self.say(foo()) # produces "[]"; correct output is "[5]"
self.say(foo()) # produces "[]"; correct output is "[5, 5]"
self.say(foo()) # produces "[]"; correct output is "[5, 5, 5]"

[Nick Winter]

Now produces Atempted to invoke bookmark for [Function] @basicer