Nohup is not writing log to output file

I am using the following command to run a python script in the background:

nohup ./cmd.py > cmd.log &

But it appears that nohup is not writing anything to the log file. cmd.log is created but is always empty. In the python script, I am using sys.stdout.write instead of print to print to standard output. Am I doing anything wrong?

You can run Python with the -u flag to avoid output buffering:

nohup python -u ./cmd.py > cmd.log &

It looks like you need to flush stdout periodically (e.g. sys.stdout.flush()). In my testing Python doesn't automatically do this even with print until the program exits.