I'm not sure I agree with "If fileConfig has no delay_fh option,
fileConfig() would create the FileHandlers with delay_fh as False".
fileConfig will create the FileHandlers using the args= section entry to
pass to the constructor. Hence, by specifying True for this parameter,
you get the FileHandlers to delay opening the files. In fact you get
more control - you can specify True for some FileHandlers and False for
others.

The relevant code is in config.py in _install_handlers:

...
klass = eval(klass, vars(logging))
args = cp.get(sectname, "args")
args = eval(args, vars(logging))
h = apply(klass, args)
...