When SimFactory is run, the python interpreter compiles the human-readable python source files to bytecode and stores them as .pyc files. These would normally be synced to the remote machine along with the .py files, which is bad because the python bytecode version might not be the same on each platform. Instead, they are excluded from the sync. However, because we use rsync with its --delete-excluded option, this means that those files on the remote machine will be deleted. According to the rsync man page, "filter rules" can be used to protect certain files from being deleted due to exclusion on the remote side.