import bpy

#Get composite nodes
nodes = bpy.context.scene.node_tree.nodes
#Get indentifer of the active node
find_type = bpy.context.scene.node_tree.nodes.active.bl_rna.identifier
#loop through nodes
for node in nodes:
    #if node has the same idetifier
    if node.bl_rna.identifier == find_type:
        #select it
        node.select = True