def get_sos_step_steps(stmt):
    '''
    Extract sos_step(x) from statement
    '''
    opt_values = get_param_of_function(
        'sos_step', stmt, extra_dict=env.sos_dict.dict())
    for value in opt_values:
        if len(value) != 1:
            raise ValueError('sos_step only accept one and only one parameter')
    return [x[0] for x in opt_values]
Extract sos_step(x) from statement