import bpy
import numpy as np

import sys
 
# switch on nodes
bpy.context.scene.use_nodes = True
tree = bpy.context.scene.node_tree
links = tree.links
  
# clear default nodes
for n in tree.nodes:
    tree.nodes.remove(n)
  
# create input render layer node
rl = tree.nodes.new('CompositorNodeRLayers')      
rl.location = 185,285
 
# create output node
v = tree.nodes.new('CompositorNodeViewer')   
v.location = 750,210
v.use_alpha = False

# create output node
of_c_node = tree.nodes.new('CompositorNodeOutputFile')
of_c_node.location = 600, 200
#of_node.base_path = 
of_c_node.format.file_format = 'PNG'
 
# Links
links.new(rl.outputs[0], v.inputs[0])  # link Image output to Viewer input
links.new(rl.outputs[0], of_c_node.inputs[0])

# Define path where to save image
of_c_node.base_path = "./images_test_png"

# render
bpy.ops.render.render()
 
# get viewer pixels directly
pixels = bpy.data.images['Viewer Node'].pixels
print(len(pixels)) # size is always width * height * 4 (rgba)
 
# copy buffer to numpy array for faster manipulation
arr = np.array(pixels[:])
print('one pixel \n',arr[100:104])

#exit blender
sys.exit(0)