I think i answer myself
I am to stupid to do it like i want, with python. But, shell scripts work everywhere an i understand it in most cases. So, here is an solution for my Problem.
I use PIN 18, which Linux GPIO is 201. I pot a pullup resistor (10kOhm) to PIN 17 - 3,3V.
After this, i configure the PIN18.
echo 201 > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio201/direction
Now i can check the value
cat /sys/class/gpio/gpio201/value
The answer should be 1.
If now the PIN18 is shorted to PIN 20 (GND), the answer is 0.
A little script does it for me:
#!/bin/sh
BUTTON=201 # shutdown button
echo "$BUTTON" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio$BUTTON/direction
while true ; do
data=`cat /sys/class/gpio/gpio$BUTTON/value`
if [ "$data" -eq "0" ] ; then
shutdown -h now
else
cnt=0
fi
done