When you are in the directory /usr/lib/python2.7/dist-packages there is a module called enum:
ls | grep ^enum
enum
So when your python3 tries to import re, it has a dependency on enum, which it tries to load in it's current directory looking at sys.path, in this contect ''
is the current directory. But in that directory it is a python 2.7 module. Which is why you do not see the error when you are in any other directory.
>>> print(sys.path)
['',
'/Library/Frameworks/Python.framework/Versions/3.6/lib/python36.zip',
'/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6',
'/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/lib-
dynload',
'/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-
packages']
So you can update your sys.path or just not work in that python2.7 packages directory with python3.