You can use

obj.rotation_euler = Euler((0.3, 0.3, 0.4), 'XYZ')

If all the other track_to options are overkill. For more attribute references see the Object documentation

Here's how to set Euler rotation.

First: from mathutils import Euler

Then: obj.rotation_euler = Euler((0.3, 0.3, 0.4), 'XYZ')

If all the other track_to options are overkill. For more attribute references see the Object documentation