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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 exists(self, key):
 """ Check if the particular key exists in the storage :param key: name of the key which existence need to be checked :return: :type key str :rtype bool """

    if key in self._keystore and not self._keystore[key].is_expired:
      return True
    elif key in self._keystore and self._keystore[key].is_expired:
      self.delete(key)
      return False

    return False