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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 get_phi_variables(self, block_addr):
 """ Get a dict of phi variables and their corresponding variables. :param int block_addr: Address of the block. :return: A dict of phi variables of an empty dict if there are no phi variables at the block. :rtype: dict """


        if block_addr not in self._phi_variables_by_block:
            return dict()
        variables = { }
        for phi in self._phi_variables_by_block[block_addr]:
            variables[phi] = self._phi_variables[phi]
        return variables