MIDIHeader struct.pack() error about midiutil HOT 3 CLOSED

Actually, you just have to change it to:
struct.pack('cccc',b'M',b'T',b'h',b'd')

The same goes for the track header line.

Hi, I have the same issue and adding b's doesn't change the exception.

Traceback (most recent call last):
  File "C:\Python33\sonification.py", line 28, in <module>
    main()
  File "C:\Python33\sonification.py", line 25, in main
    print(parse(book.sheet_by_index(sheets)))
  File "C:\Python33\sonification.py", line 5, in parse
    a = MIDIFile(1)
  File "C:\Python33\lib\site-packages\midiutil\MidiFile3.py", line 695, in __init__
    self.header = MIDIHeader(numTracks)
  File "C:\Python33\lib\site-packages\midiutil\MidiFile3.py", line 649, in __init__
    self.headerString = struct.pack('cccc','M','T','h','d')
struct.error: char format requires a bytes object of length 1

This was related to the Python Version. The code in question worked under 3.0, 
but not under 3.3.

A new release has been created -- 0.89 -- which corrects this issue. Please 
download that version and let me know if you experience any issues.