def get(source_name, size, metadata_backend=None, storage_backend=None):
if storage_backend is None:<EOL><INDENT>storage_backend = backends.storage.get_backend()<EOL><DEDENT>if metadata_backend is None:<EOL><INDENT>metadata_backend = backends.metadata.get_backend()<EOL><DEDENT>metadata = metadata_backend.get_thumbnail(source_name, size)<EOL>if metadata is None:<EOL><INDENT>return None<EOL><DEDENT>else:<EOL><INDENT>return Thumbnail(metadata=metadata, storage=storage_backend)<EOL><DEDENT>
Returns a Thumbnail instance, or None if thumbnail does not yet exist.