Finding error in running demo

Hi all. I am new in FeniCS. I had installed the fenics in ubuntu18.04 as mentioned in fenics documentation. I am facing this error while running one of the demo.

Thanku in advance.

Traceback (most recent call last):
  File "demo_auto-adaptive_poisson.py", line 23, in <module>
    from dolfin import *
  File "/usr/lib/petsc/lib/python3/dist-packages/dolfin/__init__.py", line 144, in <module>
    from .fem.assembling import (assemble, assemble_system, assemble_multimesh, assemble_mixed,
  File "/usr/lib/petsc/lib/python3/dist-packages/dolfin/fem/assembling.py", line 38, in <module>
    from ufl.form import sub_forms_by_domain
ImportError: cannot import name 'sub_forms_by_domain'

See: Ubuntu 18.04 - ImportError: cannot import name 'sub_forms_by_domain' - #8 by nate