An IFF chunk, as defined in the EA IFF 85 standard, consists of a 4-byte ID field, a 4-byte length field, and the data content of the chunk, and optionally followed by a single padding null byte if required to make the total number of bytes even.

• The Chunk ID is a 4-character string that identifies the type of chunk.

• The Length is a 4-byte integer (generally in big-endian format) indicating how long the data field is.

The Chunk class allows for either reading a chunk from a file-like object or creating a chunk and writing it into a file-like object, but not both.

For reading, the Chunk class reads a single chunk from the file-like object, and is in turn a read-only file-like object for reading the contents of the chunk.

Chunk tries to determine if the underlying file-like object is seekable by via the tell operation; if that does not raise an exception, then the file-like object presented by Chunk is itself seekable.

When the Chunk is closed, the underlying file-like object is positioned to read immediately following the Chunk (and after the padding byte, if any).

For writing, the Chunk class presents a write-only file-like object for creating the contents of the chunk, as well as the setname method for assigning the Chunk ID.

For writable chunks whose underlying file-like object is not seekable, an in-memory file object is created to hold the chunk’s data; only when the chunk is closed is the in-memory file object is flushed to the underlying file-like object.

IFF files can consist of multiple top-level chunks; “container” chunk types (FORM, CAT ``, and ``LIST) contain other chunks. The Chunk class is designed to be instantiated multiple times, one after the other, for either reading or writing multiple chunks from or to a file, or from or to the content of a “container” chunk.

The parse_chunk and parse_iff_file helper methods assist in reading IFF files by automating the parsing of container chunks. parse_iff_file returns a list of chunk tuples consisting of the chunk name and chunk content; for container chunks, the chunk content is itself a list of chunk tuples.