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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 parents_from_boolRule(self,rule):
 """ Determine parents based on boolean updaterule. Returns list of parents. """

        rule_pa = rule.replace('(','').replace(')','').replace('or','').replace('and','').replace('not','')
        rule_pa = rule_pa.split()
        # if there are no parents, continue
        if not rule_pa:
            return []
        # check whether these are meaningful parents
        pa_old = []
        pa_delete = []
        for pa in rule_pa:
            if pa not in self.varNames.keys():
                settings.m(0,'list of available variables:')
                settings.m(0,list(self.varNames.keys()))
                message = ('processing of rule "' + rule
                             + ' yields an invalid parent: ' + pa
                             + ' | check whether the syntax is correct: \n'
                             + 'only python expressions "(",")","or","and","not" '
                             + 'are allowed, variable names and expressions have to be separated '
                             + 'by white spaces')
                raise ValueError(message)
            if pa in pa_old:
                pa_delete.append(pa)
        for pa in pa_delete:
            rule_pa.remove(pa)
        return rule_pa