Question

My python program receives MIDI data from a C library. Sometimes the data will look like this:

[[[[240,0,1,116]]],[[[3,100,8,1]]],[[[107,247,0,0]]]]

and sometimes it will include timestamps like this:

[[[[240,0,1,116],26738]],[[[3,100,8,1],26738]],[[[107,247,0,0],26738]]]

I need the data in an array of bytes, with the timestamp values discarded. The code I wrote to do this is:

        def convertMidiSysex(data):    
            while isinstance(data[0][0], list):
                out = []
                for index, value in enumerate(data):
                    out = out+value
                data = out

            out = array.array('B')
            for i in range(len(data)):
                if isinstance(data[i], list):
                    for j in range(len(data[i])):
                        out.append(data[i][j])
                        if out[-1] == 247:  # 0xF7 is marker to end sysex message
                            return out

I can’t help feeling that I’m doing this the hard way. Is there a better approach to this?

Answer 1

A slightly cleaner way to get what you have now:

# the entry below mixes timestamped and non-timestamped inputs
entry = [[[[240,0,1,116]]],    [[[3,100,8,1]]],
         [[[107,247,0,0]]],    [[[240,0,1,116],26738]],
         [[[3,100,8,1],26738]],[[[107,247,0,0],26738]]]

data = array.array('B')
for sublist in entry:
    for item in sublist[0][0]:
        data.append(item)
        if item == 247:
            break