old_contents: 
  import numpy as np
  
  def export_mesh(vertices, triangles, filename, mesh_name="mcubes_mesh"):
      """
      Exports a mesh in the COLLADA (.dae) format.
      
      Needs PyCollada (https://github.com/pycollada/pycollada).
      """
      
      import collada
      
      mesh = collada.Collada()
      
      vert_src = collada.source.FloatSource("verts-array", vertices, ('X','Y','Z'))
      geom = collada.geometry.Geometry(mesh, "geometry0", mesh_name, [vert_src])
      
      input_list = collada.source.InputList()
      input_list.addInput(0, 'VERTEX', "#verts-array")
      
      triset = geom.createTriangleSet(np.copy(triangles), input_list, "")
      geom.primitives.append(triset)
      mesh.geometries.append(geom)
      
      geomnode = collada.scene.GeometryNode(geom, [])
      node = collada.scene.Node(mesh_name, children=[geomnode])
      
      myscene = collada.scene.Scene("mcubes_scene", [node])
      mesh.scenes.append(myscene)
      mesh.scene = myscene
      
      mesh.write(filename)
  
new_contents: 
  import numpy as np
  
  
  def export_obj(vertices, triangles, filename):
      """
      Exports a mesh in the (.obj) format.
      """
      
      with open(filename, 'w') as fh:
          lines = []
          
          for v in vertices:
              lines.append("v {}".format(" ".join([str(p) for p in v]))
              
          for f in triangles:
              lines.append("f {}".format(" ".join([str(p) for p in v]))
          
          fh.write("\n".join(lines))
  
  
  def export_mesh(vertices, triangles, filename, mesh_name="mcubes_mesh"):
      """
      Exports a mesh in the COLLADA (.dae) format.
      
      Needs PyCollada (https://github.com/pycollada/pycollada).
      """
      
      import collada
      
      mesh = collada.Collada()
      
      vert_src = collada.source.FloatSource("verts-array", vertices, ('X','Y','Z'))
      geom = collada.geometry.Geometry(mesh, "geometry0", mesh_name, [vert_src])
      
      input_list = collada.source.InputList()
      input_list.addInput(0, 'VERTEX', "#verts-array")
      
      triset = geom.createTriangleSet(np.copy(triangles), input_list, "")
      geom.primitives.append(triset)
      mesh.geometries.append(geom)
      
      geomnode = collada.scene.GeometryNode(geom, [])
      node = collada.scene.Node(mesh_name, children=[geomnode])
      
      myscene = collada.scene.Scene("mcubes_scene", [node])
      mesh.scenes.append(myscene)
      mesh.scene = myscene
      
      mesh.write(filename)
  
subject: Update exporter.py