<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def change_password(self, user, password):
 """ Changes user password """

        if not self.__contains__(user):
            raise UserNotExists
        self.new_users[user] = self._encrypt_password(password) + "\n"