getuid() vs. geteuid() in Python

test.sh

# checkout pyintaller 
##svn co http://svn.pyinstaller.org/trunk pyinstaller && cd pyinstaller

# make Python script that prints uid, euid
printf '#!/usr/bin/env python\nimport os\nprint(os.getuid(),os.geteuid())\n' >print-uid.py

# create stand-alone executable
python pyinstaller.py -F print-uid.py

# change ownership to root
cd print-uid/dist
sudo chown root:root ./print-uid

# run as an ordinary user
./print-uid
# -> (1000, 1000) uid, euid are the same and non-root

# setuid
sudo chmod u+s ./print-uid

# run again
./print-uid
# -> (1000, 0) uid says it is an ordinary user, but euid points to root