Python 2.8 creating Diffuse BSDF in a shader node, when I want it in a surface node

Question

In Blender/Python 2.8, I can't get my code to create the surface node I want (it creates a shader node along with a surface node that I don't want). The objective is to assign an image texture to an object as seen in three related posts (1, 2 and 3):

The manual process produces the desired result by setting up the node as follows:

In Python I am attempting to do the same (code below), but the results aren't working out. First I'll show the output, then the code:

Here's the objectionable output:

And here's the node tree as created by my code; when I make the manual adjustments I note in the picture I get the final result that I want:

My flawed code is below. Before you criticize the obvious problem (that I am creating shaders), I have tried other approaches (replacing "Shader" with "Surface" and various other words) without success. I am also baffled as to why the "Principled BSDF" node appears out of nowhere.

Here's my code. Your suggestions would be highly appreciated. Thanks in advance!

matP_name='CCmat'
matP = bpy.data.materials.get(matP_name)
if matP is None:
    matP = bpy.data.materials.new(matP_name)
matP.use_nodes=True
nodes = matP.node_tree.nodes
nodeID='ShaderNodeBsdfDiffuse'
diffuse_BSDF = matP.node_tree.nodes.new(nodeID)
path=TextureFolder+TextureFilenamePost
imgTex = bpy.data.images.load(path)
node_texture = nodes.new(type='ShaderNodeTexImage')
node_texture.image = imgTex
node_texture.location = 0,200
links = matP.node_tree.links
link = links.new(node_texture.outputs[0], nodes.get('Diffuse BSDF').inputs[0])
obj=bpy.data.objects['CubeCopy1']
obj.active_material=matP

Answer 1

Small code that can bring the indication you need.

import bpy


# Clear all nodes in a mat
def clear_material( material ):
    if material.node_tree:
        material.node_tree.links.clear()
        material.node_tree.nodes.clear()

# Create a node corresponding to a defined group
def instanciate_group( nodes, group_name ):
    group = nodes.new( type = 'ShaderNodeGroup' )
    group.node_tree = bpy.data.node_groups[group_name]


materials = bpy.data.materials

mat_name = 'test'

material = materials.get( mat_name )

if not material:
    material = materials.new( mat_name )

# We clear it as we'll define it completely
clear_material( material )

material.use_nodes = True

nodes = material.node_tree.nodes
links = material.node_tree.links

output = nodes.new( type = 'ShaderNodeOutputMaterial' )

diffuse = nodes.new( type = 'ShaderNodeBsdfDiffuse' )

#With names
link = links.new( diffuse.outputs['BSDF'], output.inputs['Surface'] )
#Or with indices
#link = links.new( diffuse.outputs[0], output.inputs[0] )

Note: when you create a new material (materials.new(...)), it creates two nodes by default (principled linked to ouput).