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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 find_all(self, kw: YangIdentifier, pref: YangIdentifier = None) -> List["Statement"]: """Return the list all substatements with the given keyword and prefix. Args: kw: Statement keyword (local part for extensions). pref: Keyword prefix (``None`` for built-in statements). """

        return [c for c in self.substatements
                if c.keyword == kw and c.prefix == pref]