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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 check(self, url: str) -> Optional[dict]: """Check if data for a url has expired. Data is not fetched again if it has expired. Args: url: url to check expiration on Returns: value of the data, possibly None """

        data = self.data.get(url)
        if data:
            data = self._check_expiration(url, data)
        return data.data if data else None