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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 image_groups_download(self, image_group_id):
 """Get data file for image group with given identifier. Parameters image_group_id : string Unique image group identifier Returns ------- FileInfo Information about image group archive file on disk or None if identifier is unknown """

        # Retrieve image group to ensure that it exist
        img_grp = self.image_groups_get(image_group_id)
        if img_grp is None:
            # Return None if image group is unknown
            return None
        else:
            # Reference and information for file image group was created from
            return FileInfo(
                img_grp.data_file,
                img_grp.properties[datastore.PROPERTY_MIMETYPE],
                img_grp.properties[datastore.PROPERTY_FILENAME]
            )