Maybe your PATHEXT
environment variable is not configured to consider python scripts as executable. Check whether the PowerShell command below outputs a string with a '.PY' fragment on your computer. If not - well - add this fragment to this env. var. :)
PS C:\Users\blabla> echo $Env:PATHEXT
.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.PY
EDIT: For the above to work, of course the .py extension has to be associated with python.