distutils - script install check file existence before copy?

[bwooster47 at gmail.com]

Not sure if it is possible to do this - I know distutils has "force"
option that can be turned on/off for install_data, but is it possible
to do something somewhat complicated - have a data file named YYY,
need to copy it to share/script/YYY only if share/script/YYY does not
already exist, otherwise, need to copy YYY to share/script/YYY.new

Does anyone have any hints on how to go about doing this?