There is currently no way to simulate Q_INVOKABLE in PySide. Invokable methods
are similar to slots but they are able to return a value. For example this is
necessary when you use QWebFrame.addToJavaScriptWindowObject: otherwise the
functions you define cannot return a value to Javascript.

There was some discussion a while back on the mailing list, which didn't end
with a decision. Two proposals were made:
- define an @Invokable decorator similar to @Slot;
- or extend Slot so that if the function returns a value this value will be
returned on invokation.

Since most slots are invoked asynchronously and don't return a value, it
probably makes sense to have a different decorator to distinguish those few
methods that do return a value. If I remember past discussions correctly, one
of the goals of the PySide team was to avoid deviating from Qt if it wasn't
necessary: from that point of view keeping the Invokable/Slot distinction seems
reasonable.

What do you think?