Ha! Yes! Unfortunately I know this because of terrible reasons. Python is reference counted so copy-on-write doesn't work for this with Python objects (note: if your Python object is actually just a reference to a native object in a library all bets are off, may work or may not).
We had an issue with the service I mentioned above where VMs with ~6GB RAM weren't working, because at the point that gunicorn forked there was instantaneously >10GB RAM usage because everything got copied. We had to make sure that the data file was only loaded after the daemon fork, which unfortunately limits the benefits of that fork, part of the idea is that you do all your setup before forking so that you know you've started cleanly.
We had an issue with the service I mentioned above where VMs with ~6GB RAM weren't working, because at the point that gunicorn forked there was instantaneously >10GB RAM usage because everything got copied. We had to make sure that the data file was only loaded after the daemon fork, which unfortunately limits the benefits of that fork, part of the idea is that you do all your setup before forking so that you know you've started cleanly.