Blender: Converting textures imported from obj to emissive materials

import bpy

mats = bpy.data.materials
for mat in mats:
    mat.use_nodes = True
    tree = mat.node_tree
    links = tree.links
    for n in tree.nodes:
        tree.nodes.remove(n)

    #diffuse = tree.nodes.new("ShaderNodeBsdfDiffuse")
    diffuse = tree.nodes.new("ShaderNodeEmission")
    diffuse.location = (0,-100)

    output = tree.nodes.new("ShaderNodeOutputMaterial")
    output.location = (400, 0)

    mix = tree.nodes.new("ShaderNodeMixShader")
    mix.location = (200,0)
    mix.inputs[0].default_value = 1.0
    links.new(mix.outputs[0], output.inputs[0])

    transparent = tree.nodes.new("ShaderNodeBsdfTransparent")
    transparent.location = (0,-250)
    links.new(transparent.outputs[0], mix.inputs[1])

    threshold = tree.nodes.new("ShaderNodeMath")
    threshold.location = (0,150)
    threshold.operation = "GREATER_THAN"
    links.new(threshold.outputs[0], mix.inputs[0])

    links.new(diffuse.outputs[0], mix.inputs[2])

    textures = mat.texture_slots
    for tex in textures:
        print(tex)
        if tex and tex.texture.type=='IMAGE':
            img = tex.texture.image
            texnode = tree.nodes.new("ShaderNodeTexImage")
            texnode.location = (-200,0)
            texnode.image = img
            links.new(texnode.outputs[0],diffuse.inputs[0])
            links.new(texnode.outputs[1],threshold.inputs[0])
            break