Change value of sun light emission strength from Python console or script I need to programatically modify the value of sun light

From the picture, it seems we can code it from 

bpy.data.node_groups["Shader Nodetree"].nodes["Emission"].inputs[1].default_value = 1.2


however, the code produce an error that 

&gt;&gt;&gt; bpy.data.node_groups["Shader Nodetree"].nodes["Emission"].inputs[1].default_value = 2
Traceback (most recent call last):
  File "&lt;blender_console&gt;", line 1, in &lt;module&gt;
KeyError: 'bpy_prop_collection[key]: key "Shader Nodetree" not found'


I found a similar post it is related to changing the material, but mine question is related to the sunlight, how would i do it ?
Yes the tooltip can be a little misleading, look for the node_tree property on the lamp data object.

With the lamp as context object 

&gt;&gt; C.object
bpy.data.objects['Lamp']

&gt;&gt;&gt; C.object.data.node_tree.nodes['Emission'].inputs['Strength'].default_value = 2


# or via bpy.data (D)

&gt;&gt;&gt; D.objects['Lamp'] == C.object
True

&gt;&gt;&gt; D.objects['Lamp'].data
bpy.data.lamps['Lamp']

&gt;&gt;&gt; lamp = D.lamps['Lamp']

&gt;&gt;&gt; lamp.node_tree.nodes['Emission'].inputs['Strength'].default_value = 3