Python: Start new command prompt on Windows and wait for it finish/exit

I don’t understand why it’s so hard to do this on Windows.

I want to spawn a bunch of command prompt windows which will run other scripts. The reason I want this is so I can see all the output from each script neatly (if I have them just be threads/subprocesses in the main window I can’t view all the output properly). I also don’t want to log the output because it’s mostly for viewing progress bars, which don’t really work with log files.

So individual parts of my requirements work, but not together:

os.system("start cmd /c {command here}")     # Launches in new command prompt, closes when done

However, os system won’t let me wait until the command finishes (since start is the actual command, the second it opens the new command prompt it’s “done”)

Similarly if I try:

p = subprocess.Popen(["start", "cmd", "/k", "{command here}"], shell = True) # Needs to be shell since start isn't an executable, its a shell cmd
p.wait()    # I can wait until finished (although it too finishes after start finishes)

So how do I do this? I read somewhere that a solution could be to use processgroup but it’s unix only….or something like that

Or if you have a neat way of displaying the output from all the subprocesses in a single window, then I don’t need to open a new command prompt and can simply use threads. That works too, but if I have lets say 4 threads downloading something and displaying a progress bar as well as outputting other information I don’t know how to display that in a way that can be read (as well as avoiding them all colliding with each other).

PS: This is on Windows Vista.
PPS: I’d preferably like a solution that works on Windows, Linux and Mac, I’m focusing on Windows for now but I’d like a solution that works for all three, and I know Windows is the most finicky. I would just substitute “the start cmd /c” for the OS appropriate command.