Imports the given FBX model, Decimates the meshes and exports as FBX

decimator.py

import bpy
import os
import sys

'''
Imports the given FBX model, Decimates the meshes and exports as FBX

@input
<input_fbx_filepath>

@output
decimated mesh as FBX file

'''

class Decimator:
    def __init__(self, fbx_file):
        self.clean_scene()
        bpy.ops.import_scene.fbx(filepath=fbx_file)
        mesh = bpy.context.selected_objects[0]
        self.simplifymesh(mesh)
        self.export_fbx(mesh,fbx_file)

    def clean_scene(self):
        bpy.ops.object.mode_set(mode='OBJECT')
        bpy.ops.object.select_by_type(type='MESH')
        bpy.ops.object.delete(use_global=False)

        for item in bpy.data.meshes:
            bpy.data.meshes.remove(item)


    def simplifymesh(self, mesh):  
        bpy.context.view_layer.objects.active = mesh        
        mod = mesh.modifiers.new(name='Decimate', type='DECIMATE')        
        bpy.context.object.modifiers['Decimate'].use_collapse_triangulate = True        
        nfaces = len(mesh.data.polygons)
        print('INPUT FACE COUNT:', nfaces)
        if nfaces > 10000:            
            ratio = 10000 / float(nfaces)        
            mod.ratio = float('%s' % ('%.6g' % (ratio)))        
            print('ratio: ', mod.ratio)
            bpy.ops.object.modifier_apply(modifier=mod.name)
        print('OUTPUT FACE COUNT:', len(mesh.data.polygons))

    def export_fbx(self, mesh, fbx_file):        
        outpath = os.path.dirname(fbx_file)
        (outfile, ext) = os.path.splitext(fbx_file)
        if not os.path.isdir(outpath): os.makedirs(outpath)
        output_fbx = os.path.join(outpath, outfile + "_decimated.fbx")
        print('EXPORTING', output_fbx)
        bpy.ops.object.select_all(action='DESELECT')
        mesh.select_set(state=True)
        bpy.ops.export_scene.fbx(filepath=output_fbx)

fbx_file = sys.argv[-1]

print('args: ', fbx_file)
blender = Decimator(fbx_file)