urdf ImportError: No module named 're'

edit

When I tried to typing as follow, to make my first urdf file:

rosrun xacro xacro.py `rospack find pr2_description`/robots/pr2.urdf.xacro -o /tmp/pr2.urdf

I got an error as follow:

Traceback (most recent call last):
  File "/opt/ros/kinetic/share/xacro/xacro.py", line 55, in <module>
    import xacro
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/xacro/__init__.py", line 39, in <module>
    import re
  File "/usr/lib/python3.5/re.py", line 123, in <module>
    import sre_compile
ImportError: No module named 'sre_compile'
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 53, in apport_excepthook
    if not enabled():
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 24, in enabled
    import re
ImportError: No module named 're'

Original exception was:

Traceback (most recent call last):
  File "/opt/ros/kinetic/share/xacro/xacro.py", line 55, in <module>
    import xacro
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/xacro/__init__.py", line 39, in <module>
    import re
  File "/usr/lib/python3.5/re.py", line 123, in <module>
    import sre_compile
ImportError: No module named 'sre_compile'

I think it is because import re call the python3, but I don't know how to fix it to call python2 to import re. So, please tell me how to solve the problem?