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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 unlock(self, password = None, keyfile = None, buf = None):
 """Unlock the database. masterkey is needed. """


        if ((password is None or password == "") and (keyfile is None or
             keyfile == "")):
            raise KPError("A password/keyfile is needed")
        elif ((type(password) is not str and password is not None) or
              (type(keyfile) is not str and keyfile is not None)):
            raise KPError("password/keyfile must be a string.")
        if keyfile == "":
            keyfile = None
        if password == "":
            password = None
        self.password = password
        self.keyfile = keyfile
        return self.load(buf)