I myself have been fighting the never ending battle between python and .dts exporting on a mac. this is often a really tough thing to trouble shoot. I'll give it a try, but if you could give alittle more insight on your machine, i may be able to help even more. (I.E. OS version, power-Pc or intel. etc.)
but for starters:
did you install python prior to installing blender? this can sometimes cause issues.
Suggestion 1: Start from scratch
uninstall blender and use a cleaning agent (I recommend CleanMyMac, its a really handy little app.) use a cleaning agent or else all of the mac .plists wil float around and you'll run into the same error. plists are the mac version of registries,
reinstall Python. you can just reinstall it right over the top. the entire python codec will get updated and overwritten.
Reboot your Machine. this will set the python Codec in the place it needs to be. if you don't reboot the whole process may work, but because the python is a script library, sometimes a boot is required to give the file precedence.
reinstall Blender, and then reinstall the .dts Exporter.
Reboot the computer again. i know this is a tad facetious, but this will get blender all squared away and in working order. any time that you apply a plugin to a program you should reboot the machine, this is just to keep everything in order, and to also let blender clean up after itself and remove the installer files.
Fire up blender. and check to see if .dts is available.
I hope that works for you.
happy modeling if it does.
