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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_variables(self, sort=None, collapse_same_ident=False):
 """ Get a list of variables. :param str or None sort: Sort of the variable to get. :param collapse_same_ident: Whether variables of the same identifier should be collapsed or not. :return: A list of variables. :rtype: list """


        variables = [ ]

        if collapse_same_ident:
            raise NotImplementedError()

        for var in self._variables:
            if sort == 'stack' and not isinstance(var, SimStackVariable):
                continue
            if sort == 'reg' and not isinstance(var, SimRegisterVariable):
                continue
            variables.append(var)

        return variables