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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 get_file(self, key, file):
 """Write contents of key to file Like :meth:`.KeyValueStore.put_file`, this method allows backends to implement a specialized function if data needs to be written to disk or streamed. If *file* is a string, contents of *key* are written to a newly created file with the filename *file*. Otherwise, the data will be written using the *write* method of *file*. :param key: The key to be read :param file: Output filename or an object with a *write* method. :raises exceptions.ValueError: If the key is not valid. :raises exceptions.IOError: If there was a problem reading or writing data. :raises exceptions.KeyError: If the key was not found. """

        self._check_valid_key(key)
        if isinstance(file, str):
            return self._get_filename(key, file)
        else:
            return self._get_file(key, file)