Fix: property "copy" returns no real copy

[Amper]

class ArgsList(object):
    def __init__(self, args=None): 
        self._args = args or []
    @property
    def all(self): 
        return self._args
    @property
    def copy(self): 
        return ArgsList(self.all)

my_args = ArgsList([1,2,3,4,5])
tmp_args = my_args.copy
tmp_args.all[0] = 999

print(my_args.all)  # [999, 2, 3, 4, 5] - OOPS!