OSX : Defining a new URL handler that points straight at a Python script

I'm trying to define a new URL handler under OSX that will point at a python script.

I've wrapped the Python script up into an applet (right-clicked on the .py, and gone Open With -> Build Applet)

I've added the following into the applet's Info.plist:

<key>CFBundleURLTypes</key>
<array>
    <dict>
        <key>CFBundleURLName</key>
        <string>Do My Thing</string>
        <key>CFBundleURLSchemes</key>
        <array>
            <string>dmt</string>
        </array>
    </dict>
</array>

I've also used the More Internet preferences pane to specify "dmt" as a protocol, but when I try to get it to link the protocol to my applet, it says that "There was a problem setting the app as the helper"

Anyone know where I should go from here?

Thanks