Back to module index

Go to module by name

chunk

Simple class to read IFF chunks.

An IFF chunk (used in formats such as AIFF, TIFF, RMFF (RealMedia File
Format)) has the following structure:

+----------------+
| ID (4 bytes)   |
+----------------+
| size (4 bytes) |
+----------------+
| data           |
| ...            |
+----------------+

The ID is a 4-byte string which identifies the type of chunk.

The size field (a 32-bit value, encoded using big-endian byte order)
gives the size of the whole chunk, including the 8-byte header.

Usually an IFF-type file consists of one or more chunks.  The proposed
usage of the Chunk class defined here is to instantiate an instance at
the start of each chunk and read from the instance until it reaches
the end, after which a new instance can be instantiated.  At the end
of the file, creating a new instance will fail with an EOFError
exception.

Usage:
while True:
    try:
        chunk = Chunk(file)
    except EOFError:
        break
    chunktype = chunk.getname()
    while True:
        data = chunk.read(nbytes)
        if not data:
            pass
        # do something with data

The interface is file-like.  The implemented methods are:
read, close, seek, tell, isatty.
Extra methods are: skip() (called by close, skips to the end of the chunk),
getname() (returns the name (ID) of the chunk)

The __init__ method has one required argument, a file-like object
(including a chunk instance), and one optional argument, a flag which
specifies whether or not chunks are aligned on 2-byte boundaries.  The
default is 1, i.e. aligned.

Classes

Chunk

close(self)

getname(self)

  Return the name (ID) of the current chunk.

getsize(self)

  Return the size of the current chunk.

isatty(self)

read(self, size=-1)

  Read at most size bytes from the chunk.
          If size is omitted or negative, read until the end
          of the chunk.
        

seek(self, pos, whence=0)

  Seek to specified position into the chunk.
          Default position is 0 (start of chunk).
          If the file is not seekable, this will result in an error.
        

skip(self)

  Skip the rest of the chunk.
          If you are not interested in the contents of the chunk,
          this method should be called so that the file points to
          the start of the next chunk.
        

tell(self)