How can I see the actual numerical output RGB values of the cycles 'Blackbody' node? (preferably through api) More generally, using the Blackbody node as an example, how can I access the current numerical values of inputs, parameters/settings and outputs of cycles nodes, through the api or by other means?

In this particular case I want to compare the conversion values calculated by the Blackbody node with other color temperature -> RGB algorithms. But I'm interested in the more general situation. If this is not possible, shouldn't it be, and will it be in the future?
Example for the compositor node which is present by default:

import bpy

scene = bpy.context.scene
scene.use_nodes = True

nt = scene.node_tree

#get the node
node = nt.nodes['Composite']

#access by string key in 2.69
input = node.inputs['Alpha'].default_value = 0.5

#older versions of blender might require
#access by index
for index, input in enumerate(node.inputs):
    if input.name == "Alpha":
        print(index)
        break

#link    
output = nt.nodes['Render Layers'].outputs['Alpha']
nt.links.new(input, output)


You can hover over the input with python tooltips enabled:


Using python it is only possible to setup the tree and its parameters.

Via OSL you can implement your own shaders. Enable Open Shading Language in the render menu, add a script node and see Text Editor -> Templates -> Open Shading Language

Template Temperature To RGB


shader temperature_to_rgb(
    float Kelvin = 1200.0,
    output color Color = 0.8)
{   
    /* Kelvin to RGB */
    Color = blackbody(Kelvin);
}


As you can see blackbody is an inbuilt function of the standard library.