ImportError: cannot import name '_remove_dead_weakref'

pip3
Traceback (most recent call last):
  File "/usr/local/bin/pip3", line 7, in 
    from pip import main
  File "/usr/local/lib/python3.5/site-packages/pip/__init__.py", line 4, in 
    import locale
  File "/usr/local/lib/python3.5/locale.py", line 19, in 
    import functools
  File "/usr/local/lib/python3.5/functools.py", line 23, in 
    from weakref import WeakKeyDictionary
  File "/usr/local/lib/python3.5/weakref.py", line 12, in 
    from _weakref import (
ImportError: cannot import name '_remove_dead_weakref'

原因：

Python版本冲突。查一下有几个，卸载掉不用的即可。