If you use pyenv, and have installed or updated Pyenv and built Python 2.x after Feb 17 or rolled your own Python 2.x by hand, you may experience an issue where some packages will fail to run with an error message like the following:

Traceback (most recent call last):

File "/Users/jasonmyers/.virtualenvs/test2/bin/jupyter-notebook", line 7, in 
from notebook.notebookapp import main
File "/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/notebook/
notebookapp.py", line 32, in 
from zmq.eventloop import ioloop
File "/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/
__init__.py", line 66, in 
from zmq import backend
File "/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/backend/
__init__.py", line 40, in 
File "/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/backend/
__init__.py", line 27, in 
_ns = select_backend(first)
File "/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/backend/
select.py", line 27, in select_backend
mod = __import__(name, fromlist=public_api)
File "/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/backend/cython/
__init__.py", line 6, in 
from . import (constants, error, message, context,
ImportError: dlopen(/Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/
backend/cython/constants.so, 2): Symbol not found: _PyUnicodeUCS2_DecodeUTF8
Referenced from: /Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/backend/
Expected in: flat namespace
in /Users/jasonmyers/.virtualenvs/test2/lib/python2.7/site-packages/zmq/backend/cython/constants.so

This is due to the fact that recently python wheel packages switched to “wide” unicode (ucs4) via PEP-513. Since not all of the wheel packages have been updated, you can end up with package that use “narrow” unicode (ucs2). I’ve seen this in jupyter, ipython, Pillow, and other Python packages. To fix this you need to install the packages without using the wheels until they release an update. For example: pip install --no-use-wheel jupyter This will take much longer to do the install; however, jupyter will work properly after being installed this way. More details at https://github.com/yyuu/pyenv/issues/257.