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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(self, blob_hash):
 """ get an object from external store. Does not need to check whether it's in the table. """

        if blob_hash is None:
            return None
        store = blob_hash[STORE_HASH_LENGTH:]
        store = 'external' + ('-' if store else '') + store

        cache_folder = config.get('cache', None)

        blob = None
        if cache_folder:
            try:
                with open(os.path.join(cache_folder, blob_hash), 'rb') as f:
                    blob = f.read()
            except FileNotFoundError:
                pass

        if blob is None:
            spec = self._get_store_spec(store)
            if spec['protocol'] == 'file':
                full_path = os.path.join(spec['location'], self.database, blob_hash)
                try:
                    with open(full_path, 'rb') as f:
                        blob = f.read()
                except FileNotFoundError:
                    raise DataJointError('Lost access to external blob %s.' % full_path) from None
            elif spec['protocol'] == 's3':
                try:
                    blob = S3Folder(database=self.database, **spec).get(blob_hash)
                except TypeError:
                    raise DataJointError('External store {store} configuration is incomplete.'.format(store=store))
            else:
                raise DataJointError('Unknown external storage protocol "%s"' % spec['protocol'])

            if cache_folder:
                if not os.path.exists(cache_folder):
                    os.makedirs(cache_folder)
                safe_write(os.path.join(cache_folder, blob_hash), blob)

        return unpack(blob)