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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 _should_set(self, key, mode):
 """ Determine if it is okay to set a key. If the mode is None, returns True, otherwise, returns True of false based on the value of ``key`` and the ``mode`` (nx | xx). """


        if mode is None or mode not in ["nx", "xx"]:
            return True

        if mode == "nx":
            if key in self.redis:
                # nx means set only if key is absent
                # false if the key already exists
                return False
        elif key not in self.redis:
            # at this point mode can only be xx
            # xx means set only if the key already exists
            # false if is absent
            return False
        # for all other cases, return true
        return True