MIDI status bytes (the first byte of the message) must have the high (0x80) bit set. the linked chart is a bit confusing, but I'm guessing 0x74 is a data byte and must be preceded by the proper status byte.
>>> import pygame.midi as midi
>>> midi.init()
>>> midiout = midi.Output(0)
>>> midiout.write_short(0xb0, 0x74, 124)
some basic MIDI documentation: http://www.midi.org/techspecs/midimessages.php
control change is 0xbn, where n is the channel number, so 0xb0 is a control change message for channel 0.