riff_parser.py

import struct

# Return a RIFF file

class LIST:
    def __init__(self, name, f):
        # contains a type and a list of subchunks.
        self.offset = f.tell() - 4
        self.name = name.decode()
        size = struct.unpack('I', f.read(4))[0]
        self.ctype = f.read(4).decode()
        self.sub = []
        # recursive fill chunks
        while f.tell() < self.offset + size:
            name = f.read(4)
            if name in (b'RIFF',b'LIST'):
                self.sub.append( LIST( name, f ) )
            else:
                self.sub.append( CHUNK( name, f ) )
    def __repr__(self):
        r = f'<LIST {self.name}/{self.ctype} with {len(self.sub)} chunks>\n'
        for s in self.sub:
            r += f'  {s}\n'
        return r
    def size(self):
        return 4 + sum(8 + s.size() for s in self.sub)
    def write( self, f ):
        f.write( self.name.encode() )
        f.write( struct.pack('I', self.size() ) )
        f.write( self.ctype.encode() )
        for s in self.sub:
            s.write( f )

class CHUNK:
    def __init__(self, name, f):
        self.name = name.decode()
        size = struct.unpack('I', f.read(4))[0]
        self.data = f.read(size)
    def __repr__(self):
        return f'<CHUNK {self.name} with {len(self.data)} bytes>'
    def set_data( self, data ):
        self.data = data
        if len(data) % 2:
            self.data += b'\x00'
    def size(self):
        return len(self.data)
    def write(self, f):
        f.write( self.name.encode() )
        f.write( struct.pack('I', len(self.data)) )
        f.write( self.data )

def dump(tree, nest=0):
    tab = '  '*nest
    if isinstance(tree,LIST):
        print( tab+'LIST', tree.name, tree.ctype, 'contains', len(tree.sub), 'chunks' )
        for s in tree.sub:
            dump( s, nest+1 )
    else:
        print( tab+'CHUNK', tree.name, 'contains', len(tree.data), 'bytes')

def test():
    # Read the whole file.
    f = open('/dev/CueManager/Whistle.wav','rb')
    name = f.read(4)
    assert name == b'RIFF'
    tree = LIST(name, f)

    dump(tree)
    print(tree.sub[1].sub[0].data)
    print(tree.size())

    # Change the info chunk.

    tree.sub[1].sub[0].set_data( b"New Info\x00" )
    print(tree.size())

    tree.write( open('xxx.wav','wb') )

test()

Thank you! I'm from the stackoverflow question, by the way. Another question, what is the licensing of this code?