Why does desktop.getCurrentComponent() return None in PyUNO?

Question

Trying to revive a PyUNO sample script called Wavelet to learn how LO works nowadays and get re-started. Since LibreOffice & UNO changed a bit from the script's creation time I am running into problems.

Managed to get the desktop object. Now I want to retrieve the open document's component. How do I achieve this properly? The desktop.getCurrentComponent() call returns None.

LibreOffice version: 6.4.6.2.

System: Ubuntu MATE 20.04 x86_64.

The code follows:

#!/usr/bin/python3

def TestWave(event):
    wavelet = Wavelet(XSCRIPTCONTEXT)
    wavelet.trigger( () )

import uno
import unohelper
import string
from com.sun.star.task import XJobExecutor

class Wavelet( unohelper.Base, XJobExecutor ):
    def __init__( self, ctx ):
        self.ctx = ctx

    def trigger( self, args ):
        desktop = self.ctx.ServiceManager.createInstanceWithContext(
            "com.sun.star.frame.Desktop", self.ctx )

        doc = desktop.getCurrentComponent()
        print('doc:', doc)

        #try:
        search = doc.createSearchDescriptor()
        search.SearchRegularExpression = True
        search.SearchString = "\\<(k|s|v|z|o|u|i|a) "

        found = doc.findFirst( search )
        while found:
            print("found:", found.String)
            found.String = string.replace( found.String, " ", u"\xa0" )
            found = doc.findNext( found.End, search)

        #except:
        #    pass


g_ImplementationHelper = unohelper.ImplementationHelper()
g_ImplementationHelper.addImplementation(
        Wavelet,
        "name.vojta.openoffice.Wavelet",
        ("com.sun.star.task.Job",),)

if __name__ == "__main__":
    import os
    # Start OpenOffice.org, listen for connections and open testing document
    os.system( "loffice '--accept=socket,host=localhost,port=2002;urp;' --writer ./WaveletTest.odt &" )
    # Get local context info
    localContext = uno.getComponentContext()
    resolver = localContext.ServiceManager.createInstanceWithContext(
      "com.sun.star.bridge.UnoUrlResolver", localContext )
    ctx = None
    # Wait until the OO.o starts and connection is established
    while ctx == None:
      try:
        ctx = resolver.resolve(
          "uno:socket,host=localhost,port=2002;urp;StarOffice.ComponentContext" )
      except:
        pass
    # Trigger our job
    wavelet = Wavelet( ctx )
    wavelet.trigger( () )

Output:

doc: None
Traceback (most recent call last):
  File "./wavelet.py", line 62, in <module>
    wavelet.trigger( () )
  File "./wavelet.py", line 24, in trigger
    search = doc.createSearchDescriptor()
AttributeError: 'NoneType' object has no attribute 'createSearchDescriptor'

Edit 1

Cross posted at the following address: https://ask.libreoffice.org/en/question/283785/why-does-desktopgetcurrentcomponent-return-none-in-pyuno/

Answer 1

Tried to wait until the document component becomes available. And it worked:

doc = None
while doc is None:
    doc = desktop.getCurrentComponent()