I'm having trouble finishing the QGIS tutorial for Using Custom Python Expression Functions: http://www.qgistutorials.com/de/docs/custom_python_functions.html
I get to the point where I write the script in the function editor, but when I want to use the function in an expression it looks different and doesn't work.
Screenshot 1 is what it looks like in the tutorial, screenshot 2 is my result when I double click on the custom function. The code is the same, I copy pasted it into the functions editor. When I write the exact same expression as in the tutorial it says 'expression invalid' (screenshot 3).