pip升级报错 ImportError: cannot import name 'main'

root@ubuntu-virtual-machine:/usr/bin# pip3 install pyaudio
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in <module>
    from pip import main
ImportError: cannot import name 'main'

参考：https://stackoverflow.com/questions/28210269/importerror-cannot-import-name-main-when-running-pip-version-command-in-windo