After installing NEST ubuntu 18.04 live media (lubuntu-18.04_nest-2.18.0.ova downloaded a few days ago), I get the following error message but am able to import nest in python3 ok:
nest@nestvm:~$ python3
Python 3.6.8 (default, Jan 14 2019, 11:02:34) 
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pyNN.nest as sim
[INFO] [2019.8.21 14:31:47 /home/nest/work/nest-simulator-2.18.0/nestkernel/rng_manager.cpp:217 @ Network::create_rngs_] : Creating default RNGs
[INFO] [2019.8.21 14:31:47 /home/nest/work/nest-simulator-2.18.0/nestkernel/rng_manager.cpp:260 @ Network::create_grng_] : Creating new default global RNG

              -- N E S T --
  Copyright (C) 2004 The NEST Initiative

 Version: nest-2.18.0
 Built: Jul  2 2019 15:09:55

 This program is provided AS IS and comes with
 NO WARRANTY. See the file LICENSE for details.

 Problems or suggestions?
   Visit https://www.nest-simulator.org

 Type 'nest.help()' to find out more about NEST.

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/dist-packages/pyNN/nest/__init__.py", line 18, in <module>
    from . import simulator
  File "/usr/local/lib/python3.6/dist-packages/pyNN/nest/simulator.py", line 257, in <module>
    state = _State()  # a Singleton, so only a single instance ever exists
  File "/usr/local/lib/python3.6/dist-packages/pyNN/nest/simulator.py", line 59, in __init__
    self.verbosity = "warning"
  File "/usr/local/lib/python3.6/dist-packages/pyNN/nest/simulator.py", line 120, in _set_verbosity
    nest.sli_run("M_%s setverbosity" % verbosity.upper())
AttributeError: module 'nest' has no attribute 'sli_run'
Any suggestions?