With the following line you can list all function definitions that are obviously not used as an attribute, a function call, a decorator or a return value. So it is approximately what you are looking for. It is not perfect, it is slow, but I never got any false positives. (With linux you have to replace ack with ack-grep)
for f in $(ack --python --ignore-dir tests -h --noheading "def ([^_][^(]*).*\):\s*$" --output '$1' | sort| uniq); do c=$(ack --python -ch "^\s*(|[^#].*)(@|return\s+|\S*\.|.*=\s*|)"'(?
