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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 has(self, key, mtime=None):

 """
 This method should almost NEVER be used. The reason is that between the time
 has_key is called, and the key is accessed, the key might vanish.
 
 """

        v = self.__values.get(key, None)
        if not v:
            return False
        if self.check_modified_time:
            mtime = self._get_mtime(key, mtime)
            if mtime != self.__modified_times[key]:
                del self[key]
                return False
        return True