Cygwin64 /usr/bin/env: ‘python3’: No such file or directory

Welcome aboard! Python 3 isn’t loaded by default in cygwin, nor is lxml so you need to run cygwin setup and select both (they will likely pull in a bunch of dependencies as well):

python3:

lxml

As well FritzingCheckPart.py assumes you are familiar with the structure of the svg files so this set of tutorials may be helpful as well:

Peter