在ubuntu系统下，系统默认python2.7和python3.5，但需要使用更高的python版本的pip3时可能遇到的错误
问题一：
Traceback (most recent call last):
File "/usr/bin/pip3", line 9, in <module>
from pip import main
ImportError: cannot import name 'main'
解决办法：
sudo vim /usr/bin/pip3
修改：
from pip import main
if __name__ == '__main__':
sys.exit(main())
为：
from pip import __main__
if __name__ == '__main__':
sys.exit(__main__._main())
注意：单下划线和双下划线
问题二：
使用pip3安装任何模块时的类似报错：
Traceback (most recent call last):
File "/usr/bin/pip3", line 11, in <module>
sys.exit(__main__._main())
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_internal/__init__.py", line 246, in main
return command.main(cmd_args)
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_internal/basecommand.py", line 264, in main
timeout=min(5, options.timeout)) as session:
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_internal/basecommand.py", line 81, in _build_session
insecure_hosts=options.trusted_hosts,
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_internal/download.py", line 338, in __init__
self.headers["User-Agent"] = user_agent()
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_internal/download.py", line 101, in user_agent
zip(["name", "version", "id"], distro.linux_distribution()),
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_vendor/distro.py", line 120, in linux_distribution
return _distro.linux_distribution(full_distribution_name)
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_vendor/distro.py", line 634, in linux_distribution
self.version(),
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_vendor/distro.py", line 688, in version
self.lsb_release_attr('release'),
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_vendor/distro.py", line 836, in lsb_release_attr
return self._lsb_release_info.get(attribute, '')
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_vendor/distro.py", line 522, in __get__
ret = obj.__dict__[self._fname] = self._f(obj)
File "/usr/bin/python3.6/lib/python3.6/site-packages/pip/_vendor/distro.py", line 933, in _lsb_release_info
stdout = subprocess.check_output(cmd, stderr=devnull)
File "/usr/bin/python3.6/lib/python3.6/subprocess.py", line 336, in check_output
**kwargs).stdout
File "/usr/bin/python3.6/lib/python3.6/subprocess.py", line 418, in run
output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '('lsb_release', '-a')' returned non-zero exit status 1.
解决办法：
sudo vim /usr/bin/lsb_release
修改第一行，指明python的版本号，若安装的是python3.6则修改：
#!/usr/bin/python3
为：
#!/usr/bin/python3.6