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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 _rules_from_env(self, val):
 """Transforms rules list from env-string to python."""

        val = val.split(':')
        if 'DEFAULT_RULES' in val:
            val = const.DEFAULT_RULES + [rule for rule in val if rule != 'DEFAULT_RULES']
        return val