Use F5 REST API Python SDK to update an external datagroup

I have working code using the F5 Python REST SDK that can upload a txt file and create an external datagroup from it.   

But I cannot figure out how to use the API to update that datagroup file without deleting the datagroup and recreating it.

All of the examples I can find (e.g. https://devcentral.f5.com/s/question/0D51T00006i7j1ySAA/upload-programatically-external-data-group-file) do the following:

• create a datagroup file object from a sourcepath
• create a datagroup object from the datagroup file object
• display the created object's attributes

Then they delete the datagroup object and datagroup file object so that they can run again.  

I cannot find a way to reload the data from an updated data file into an existing datagroup object.

I have also seen code that can walk a datagroup and update items in it one by one, but I'd really like to use a file update model.

Any ideas?  Code sample follows:

from f5.bigip import ManagementRoot


# Connect to the BigIP
mgmt = ManagementRoot("IP-FIXME", "USER-FIXME", "PASSWD-FIXME")


def showDatagroups() :


  print("\n\n**** Showing Datagroups")
  dgs = mgmt.tm.ltm.data_group.externals.get_collection()
  for idx, dg in enumerate(dgs):
    print("\n{}: {}".format(idx, dg.raw))
    print("\n{}: {}".format(idx, dg.name))
    if hasattr(dg, 'records'):
      print("\n{}: {}".format(idx, dg.records))
      for record in dg.records:
        print("\nrec: {}".format(record))
    else:
      print("\nObject {} has no records".format(dg.name))




def showDatagroupFiles():
  print("\n\n**** Showing DatagroupFiles")
  dgFiles = mgmt.tm.sys.file.data_groups.get_collection()
  for idx, f in enumerate(dgFiles):
    print('\n{}: {}'.format(idx, f.raw))




def uploadFile(f):
  # This upload works - it places the file in the uploads folder.
  # But I cannot seem to access the file uploaded file with the datagroup create method
  print("\n\n**** Uploading datagroup file {}".format(f))
  mgmt.shared.file_transfer.uploads.upload_file(f)


def createDatagroupFile(source_path, dgname, dataType):
  print("\n\n**** Creating datagroup file {}, name {}, type {}".format(fname, dgname, dataType))
  # check first if its there
  dgFiles = mgmt.tm.sys.file.data_groups.get_collection()
  found = 0
  for idx, f in enumerate(dgFiles):
    if f.name == dgname:
      found = 1
      break


  if found:
    print("File {} already exists".format(dgname))
    #  Here's where I would just update the file if I could
  else:
    print("Creating DG File {} from fname {}".format(dgname, sourcePath))
    dgFile = mgmt.tm.sys.file.data_groups.data_group.create(sourcePath=source_path, name=dgname, type=dataType)


def createDatagroupFromFile(name, file):
  print("\n\n**** Creating datagroup {} from file {}".format(name, file))
  # check first if its there
  dgs = mgmt.tm.sys.file.data_groups.get_collection()
  found = 0
  for idx, dg in enumerate(dgs):
    if dg.name == name:
      found = 1
      break


  if found:
    print("Datagroup {} already exists".format(name))
    #  Here's where I would just update the datagroup if I could
  else:
    dgObject = mgmt.tm.ltm.data_group.externals.external.create(name=name, externalFileName=file)


if __name__ == "__main__":


  fname = './dg_test5.txt'
  # using HTTP server for raw file - this is the only way I could get the upload to work
  sourcePath = 'http://127.0.0.1:8000/dg_test5.txt'
  dgfilename = 'dg_test5.txt'
  dgname = 'dg_test5'


  uploadFile(fname)


  createDatagroupFile(sourcePath, dgfilename, 'string')


  createDatagroupFromFile(dgname, dgfilename)


  showDatagroups()


  showDatagroupFiles()