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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 load_stack(stack):
 """ Loads the saved state of a CallStack and returns a whole instance given an instance with incomplete state. :param caliendo.hooks.CallStack stack: The stack to load :returns: A CallStack previously built in the context of a patch call. :rtype: caliendo.hooks.CallStack """

    global CACHE_
    load_cache(True)
    key = "{0}.{1}".format(stack.module, stack.caller)
    if key in CACHE_['stacks']:
        return pickle.loads(CACHE_['stacks'][key])