Reading Structure Binary Data in Python?

Maybe you are looking for Construct, a pure-Python 2 & 3 binary parsing library?

Python's struct module works like this:

record_header = struct.Struct("<cb") 
warning = struct.Struct("<iii128")
info = struct.Struct("<iiiii")

while True:
    header_text = input.read(record_header.size)
    # file is empty
    if not header_text:
       break
    packet_type, extra_data = record_header.unpack(header_text)
    if packet_type == 'w':
        warning_data = warning.unpack( input.read(warning.size) )
    elif packet_type == 'i':
        info_data = info.unpack( input.read(info.size) )

See the documentation for details: http://docs.python.org/library/struct.html

The struct module would probably work, but you might also use the python bindings for Google's protocol buffers.

I would like to give an example for how to do reading in python.

typedef struct {
    ID             chunkname;
    long           chunksize;

    /* Note: there may be additional fields here, depending upon your data. */

} Chunk;

How you read this struct data from file in python? Here is one way:

class Chunk:
def __init__(self, file, align=True, bigendian=True, inclheader=False):
    import struct
    self.closed = False
    self.align = align      # whether to align to word (2-byte) boundaries
    if bigendian:
        strflag = '>'
    else:
        strflag = '<'
    self.file = file
    self.chunkname = file.read(4)
    if len(self.chunkname) < 4:
        # you need to take care of end of file
        raise EOFError
    try:
        # you could use unpack
        # http://docs.python.org/2/library/struct.html#format-characters
        # here 'L' means 'unsigned long' 4 standard size
        self.chunksize = struct.unpack(strflag+'L', file.read(4))[0]
    except struct.error:
        # you need to take care of end of file
        raise EOFError
    if inclheader:
        self.chunksize = self.chunksize - 8 # subtract header
    self.size_read = 0
    try:
        self.offset = self.file.tell()
    except (AttributeError, IOError):
        self.seekable = False
    else:
        self.seekable = True

So you need to understand the mapping between c structure and the format for struct.unpack() http://docs.python.org/2/library/struct.html#format-characters.