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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def save_stack(stack):
 """ Saves a stack object to a flatfile. :param caliendo.hooks.CallStack stack: The stack to save. """

    global CACHE_
    serialized = pickle.dumps(stack, PPROT)
    CACHE_['stacks']["{0}.{1}".format(stack.module, stack.caller)] = serialized
    write_out()