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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 data(self):
 """ raw image data """

        if self._data is None:
            request = urllib.Request(self._url, headers={'User-Agent': USER_AGENT})
            with contextlib.closing(self._connection.urlopen(request)) as response:
                self._data = response.read()
        return self._data