You need to know where to place your script file on the target installation (e.g. /usr/lib/myApp/plugins/myNiceScript.py)
In the spec-File (section %install) you have to copy your script under %{buildroot} into the target directory (which has to be created first.
%install
...
# in case the dir does not exist:
mkdir -p %{buildroot}/usr/lib/myApp/plugins
cp whereitis/myNiceScript.py %{buildroot}/usr/lib/myApp/plugins
At the end you have to define the file flags in the %files section. E.g. if your file has to have 644 under root:
%files
...
%defattr(644,root,root)
/usr/lib/myApp/plugins/myNiceScript.py
If your plugins directory is to be created during installation you need to define these flags too:
%defattr(755,root,root)
%dir /usr/lib/myApp/plugins