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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 set(self, key, value, expiration_dt):
 """Adds a new key value pair to the cache. Parameters key : any The key to use for the pair. value : any The value to store under the name ``key``. expiration_dt : datetime When should this mapping expire? The cache is considered invalid for dates **strictly greater** than ``expiration_dt``. """

        self._cache[key] = CachedObject(value, expiration_dt)