How to link an add-in application with web-server?

[state.of.grace.17]

I try to make an add-in for Fusion 360 where I could get a parametric assembly from web-server.  I made a try but there was an error which I have no idea how to make it solved. 
User has to click on add-in and then parametric assembly and palette should appear at the same time (custom palette is for choosing user's parameters). 
Here are the code and an error: 

import adsk.core, adsk.fusion, adsk.cam, traceback

import urllib.request

import urllib.error

import urllib.parse

import pathlib

handlers = []

app = adsk.core.Application.get()

ui  = app.userInterface

def run(context😞

    ui = None

    try:

        app = adsk.core.Application.get()

        ui  = app.userInterface

        ui.messageBox('Добавлена надстройка для соединительных муфт')

        workSpace = ui.workspaces.itemById('FusionSolidEnvironment')

        tbPanels = workSpace.toolbarPanels

        tbPanel = tbPanels.itemById('NewPanel')

        if tbPanel:

            tbPanel.deleteMe()

        tbPanel = tbPanels.add('NewPanel', 'БИБЛИОТЕКА МУФТ', 'SelectPanel', False)

        cmdDef = ui.commandDefinitions.itemById('NewCommand')

        if cmdDef:

            cmdDef.deleteMe()

        cmdDef = ui.commandDefinitions.addButtonDefinition('NewCommand', 'Создать муфту', 'Ввод параметров для соединительных муфт','.//resource')

        tbPanel.controls.addCommand(cmdDef)

        sampleCommandCreated = SampleCommandCreatedEventHandler()

        cmdDef.commandCreated.add(sampleCommandCreated)

        handlers.append(sampleCommandCreated)

    except:

        if ui:

            ui.messageBox('Failed:\n{}'.format(traceback.format_exc()))

class SampleCommandCreatedEventHandler(adsk.core.CommandCreatedEventHandler😞

    def __init__(self😞

        super().__init__()

    def notify(self, args😞

        eventArgs = adsk.core.CommandCreatedEventArgs.cast(args)

        cmd = eventArgs.command

        # Connect to the execute event.

        onExecute = SampleCommandExecuteHandler()

        cmd.execute.add(onExecute)

        handlers.append(onExecute)

class SampleCommandExecuteHandler(adsk.core.CommandEventHandler😞

    def __init__(self😞

        super().__init__()

    def notify(self, args😞

        try:

            app = adsk.core.Application.get()

            ui  = app.userInterface

            # Create and display the palette.

            palette = ui.palettes.itemById('myExport')

            if palette:

                palette.deleteMe()

            if not palette:

                #make the [close] button invisible

                palette = ui.palettes.add('myExport', 'БИБЛИОТЕКА МУФТ', 'index.html', True, True, True, 400, 200)

                # Dock the palette to the right side of Fusion window.

                palette.dockingState = adsk.core.PaletteDockingStates.PaletteDockStateRight

                url = "http://195.133.144.86:4200//Half-coupling1.f3d"

                occ = importComponentFromURL(url)

            else: 

                palette.isVisible = True 

        except:

            ui.messageBox('Command executed failed: {}'.format(traceback.format_exc()))

def importComponentFromURL(url) -> adsk.fusion.Occurrence:

    app = adsk.core.Application.get()

    ui = app.userInterface

    # doc check

    doc = app.activeDocument

    if not doc.dataFile:

        ui.messageBox('Please save the document once.')

        return adsk.fusion.Occurrence.cast(None)

    folder = pathlib.Path(r'C:\Temp')

    if not folder.exists():

        folder.mkdir()

    parsed = urllib.parse.urlparse(url)

    filename = parsed.path.split('//')[-1]

    dlFile = folder / filename

    # suffix check

    if dlFile.suffix != '.f3d':

        ui.messageBox('F3D File Only')

        return adsk.fusion.Occurrence.cast(None)

    # delete download file

    if dlFile.is_file():

        dlFile.unlink()

    # file download

    try:

        data = urllib.request.urlopen(url).read()

        with open(str(dlFile), mode="wb") as f:

            f.write(data)

    except:

        ui.messageBox(f'File not found in URL\n{url}')

        return adsk.fusion.Occurrence.cast(None)

    # import f3d

    app.executeTextCommand(u'Fusion.ImportComponent {}'.format(dlFile))

    app.executeTextCommand(u'NuCommands.CommitCmd')

    # delete download file

    if dlFile.is_file():

        dlFile.unlink()

    des = adsk.fusion.Design.cast(app.activeProduct)

    comp = des.activeComponent

    return comp.occurrences[-1]

def stop(context😞

    ui = None

    try:

        ui.messageBox('Stop addin')

        workSpace = ui.workspaces.itemById('FusionSolidEnvironment')

        tbPanels = workSpace.toolbarPanels

        tbPanel = tbPanels.itemById('NewPanel')

        if tbPanel:

            tbPanel.deleteMe()

        cmdDef = ui.commandDefinitions.itemById('NewCommand')

        if cmdDef:

            cmdDef.deleteMe()

    except:

        if ui:

            ui.messageBox('Failed:\n{}'.format(traceback.format_exc()))

[JeromeBriot]

Hello,

I guess that the problem is in the next block of code:

            if palette:
                palette.deleteMe()

The deleteMe() method deletes the palette object but it doesn't clear the palette variable. So the condition "if not palette:" is false and the code goes to the line "palette.isVisible = True". But the palette object doesn't exist anymore. So the code crashes.

A solution could be to set the variable to None:

            if palette:
                palette.deleteMe()
                palette = None

But can you explain what you're trying to do?

Please use the "Insert/Edit code sample" tool ( </> icon in the toolbar) when you write your message.

[state.of.grace.17]

Hi! We are trying to create an add-in application to design parametric assemblies (couplings). We want to get a parametric coupling assembly from web-server and put it into Fusion 360 active design (user has to choose desired parameters and then click on Build button). 

[state.of.grace.17]

We tried to use your method but we still have the same error. 

[kandennti]

Hi @state.of.grace.17 .

I'm not sure what 'index.html' is doing, but I modified it like this and the error was avoided.

・・・
class SampleCommandExecuteHandler(adsk.core.CommandEventHandler):
    def __init__(self):
        super().__init__()
    def notify(self, args):
        try:
            # app = adsk.core.Application.get()
            # ui  = app.userInterface
            # Create and display the palette.
            palette = ui.palettes.itemById('myExport')
            # if palette:
            #     palette.deleteMe()
            if not palette:
                #make the [close] button invisible
                palette = ui.palettes.add('myExport', 'БИБЛИОТЕКА МУФТ', 'index.html', True, True, True, 400, 200)

                # Dock the palette to the right side of Fusion window.
                palette.dockingState = adsk.core.PaletteDockingStates.PaletteDockStateRight

            palette.isVisible = True

            url = "http://195.133.144.86:4200//Half-coupling1.f3d"
            occ = importComponentFromURL(url)

        except:
            ui.messageBox('Command executed failed: {}'.format(traceback.format_exc()))
・・・

def importComponentFromURL(url) -> adsk.fusion.Occurrence:
・・・

    # import f3d
    app.executeTextCommand(u'Fusion.ImportComponent /NoMove {}'.format(dlFile))
    # app.executeTextCommand(u'NuCommands.CommitCmd')
・・・
def stop(context):
    # ui = None
    try:
        ui.messageBox('Stop addin')
・・・

We have also fixed the strange scope of 'ui'.