How to add drivers in node inputs in python? I am trying to add a driver in a node entry in the World.
The following script fail with 
"TypeError: bpy_struct.driver_add(): property "inputs" not animatable
"
I can't find sample of similar code. Any help?

import bpy
scn = bpy.context.scene

wd = scn.world
nodes = wd.node_tree.nodes
wd.node_tree.nodes.clear() 

DR1 = nodes.new('ShaderNodeMath')
drv = DR1.driver_add("inputs",0)
Drive the default_value property of a particular input channel.

&gt;&gt;&gt; n = C.scene.world.node_tree.nodes.new("ShaderNodeMath")
&gt;&gt;&gt; d = n.inputs[0].driver_add("default_value")

&gt;&gt;&gt; d.driver.expression
'0.5'

&gt;&gt;&gt;