You should consider upgrading via the 'pip install --upgrade pip' command

解决办法  sudo -H pip install --upgrade pip  

python -m pip install --upgrade pip
Collecting pip
  Using cached https://files.pythonhosted.org/packages/8d/07/f7d7ced2f97ca3098c16565efbe6b15fafcba53e8d9bdb431e09140514b0/pip-19.2.2-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 8.1.2
    Uninstalling pip-8.1.2:
Exception:
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/usr/lib/python2.7/site-packages/pip/commands/install.py", line 326, in run
    strip_file_prefix=options.strip_file_prefix,
  File "/usr/lib/python2.7/site-packages/pip/req/req_set.py", line 736, in install
    requirement.uninstall(auto_confirm=True)
  File "/usr/lib/python2.7/site-packages/pip/req/req_install.py", line 742, in uninstall
    paths_to_remove.remove(auto_confirm)
  File "/usr/lib/python2.7/site-packages/pip/req/req_uninstall.py", line 115, in remove
    renames(path, new_path)
  File "/usr/lib/python2.7/site-packages/pip/utils/__init__.py", line 267, in renames
    shutil.move(old, new)
  File "/usr/lib64/python2.7/shutil.py", line 302, in move
    os.unlink(src)
OSError: [Errno 13] Permission denied: '/usr/bin/pip'
You are using pip version 8.1.2, however version 19.2.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command